diff --git a/android/core/design/src/main/kotlin/se/hagstedt/kvitt/design/chart/Charts.kt b/android/core/design/src/main/kotlin/se/hagstedt/kvitt/design/chart/Charts.kt
index 0c4ea35..f7e0101 100644
--- a/android/core/design/src/main/kotlin/se/hagstedt/kvitt/design/chart/Charts.kt
+++ b/android/core/design/src/main/kotlin/se/hagstedt/kvitt/design/chart/Charts.kt
@@ -35,6 +35,7 @@ import androidx.compose.ui.geometry.RoundRect
 import androidx.compose.ui.geometry.Size
 import androidx.compose.ui.graphics.Color
 import androidx.compose.ui.graphics.Path
+import androidx.compose.ui.graphics.drawscope.DrawScope
 import androidx.compose.ui.graphics.drawscope.clipPath
 import androidx.compose.ui.platform.LocalDensity
 import androidx.compose.ui.res.stringResource
@@ -95,6 +96,112 @@ fun niceStep(maxKronor: Long): Long {
     return (factor * magnitude).toLong().coerceAtLeast(1)
 }
 
+/** The y scale of a chart: [step] kronor between gridlines and [lines] gridlines above the 0 baseline (0 when the range is empty, D-068). */
+internal class AxisScale(val step: Long, val lines: Long) {
+    /** The plot's top in öre. */
+    val topOre: Long get() = (step * lines).coerceAtLeast(1) * 100
+
+    /** Gridline [i]'s height as a fraction of the plot. */
+    fun fraction(i: Long): Float = if (lines == 0L) 0f else i.toFloat() / lines
+}
+
+/** Round gridlines for the largest value [maxOre]: [niceStep] kronor apart, enough of them to reach it. */
+internal fun axisScale(maxOre: Long): AxisScale {
+    val maxKronor = maxOre / 100
+    val step = niceStep(maxKronor)
+    val lines = if (maxKronor == 0L) 0L else ((maxKronor + step - 1) / step).coerceAtLeast(1)
+    return AxisScale(step, lines)
+}
+
+/** The y gutter: 44 dp, wider when the widest gridline label needs it (200 %). */
+@Composable
+internal fun axisGutter(scale: AxisScale): Dp {
+    val language = kvittLanguage()
+    val measurer = rememberTextMeasurer()
+    val widest = (0..scale.lines).maxOf { measurer.measure(MoneyFormatter.wholeKronor(scale.step * it, language), KvittTheme.typography.chartAxis).size.width }
+    return maxOf(KvittDimens.chartAxisGutter, with(LocalDensity.current) { widest.toDp() } + KvittTheme.spacing.s2)
+}
+
+/** The gridline labels in whole kronor, right-aligned in the [gutter]; decorative for TalkBack. */
+@Composable
+internal fun YAxisLabels(scale: AxisScale, gutter: Dp) {
+    val language = kvittLanguage()
+    val labelHeight = with(LocalDensity.current) { KvittTheme.typography.chartAxis.lineHeight.toDp() }
+    Box(Modifier.width(gutter).height(KvittDimens.chartPlot).clearAndSetSemantics { }) {
+        for (i in 0..scale.lines) {
+            Text(
+                MoneyFormatter.wholeKronor(scale.step * i, language),
+                Modifier
+                    .width(gutter - KvittTheme.spacing.s2)
+                    .offset(y = KvittDimens.chartPlot * (1 - scale.fraction(i)) - labelHeight / 2),
+                style = KvittTheme.typography.chartAxis,
+                color = KvittTheme.colors.chartAxisLabel,
+                textAlign = TextAlign.End,
+                maxLines = 1,
+            )
+        }
+    }
+}
+
+/** The 1 dp gridlines at the scale's round values (only the 0 baseline for an empty range). */
+internal fun DrawScope.drawGridlines(scale: AxisScale, color: Color) {
+    val stroke = KvittDimens.chartGridLine.toPx()
+    for (i in 0..scale.lines) {
+        val y = (size.height * (1 - scale.fraction(i))).coerceIn(stroke, size.height - stroke)
+        drawLine(color, Offset(0f, y), Offset(size.width, y), stroke)
+    }
+}
+
+/**
+ * Where a chart's buckets sit: one slot of [slotWidth] per bucket (16 dp at least, 56 at most), [spacing] apart, in
+ * [contentWidth]; [scrolls] when the slots do not fit at the minimum width.
+ */
+internal class SlotLayout(val slotWidth: Dp, val spacing: Dp, val contentWidth: Dp, val scrolls: Boolean)
+
+internal fun slotLayout(count: Int, plotWidth: Dp): SlotLayout {
+    val n = count.coerceAtLeast(1)
+    val natural = (plotWidth - KvittDimens.chartBarGap * (n - 1)) / n
+    val slot = natural.coerceIn(KvittDimens.chartMinBar, KvittDimens.chartMaxBar)
+    val scrolls = natural < KvittDimens.chartMinBar
+    val contentWidth = if (scrolls) (slot + KvittDimens.chartBarGap) * n else plotWidth
+    val spacing = if (scrolls) KvittDimens.chartBarGap else (contentWidth - slot * n) / (n.coerceAtLeast(2) - 1).coerceAtLeast(1)
+    return SlotLayout(slot, spacing, contentWidth, scrolls)
+}
+
+/** The x labels under the slots ("maj", or the week number "41"); every second one at 200 % when the slots are narrow. */
+@Composable
+internal fun XLabels(keys: List<String>, layout: SlotLayout, arrangement: Arrangement.Horizontal = Arrangement.spacedBy(layout.spacing)) {
+    val language = kvittLanguage()
+    val large = LocalDensity.current.fontScale >= KvittDimens.LARGE_FONT_SCALE
+    Row(Modifier.width(layout.contentWidth).padding(top = KvittDimens.chartXLabelTop).clearAndSetSemantics { }, horizontalArrangement = arrangement) {
+        val thin = large && layout.slotWidth < KvittDimens.chartMaxBar
+        keys.forEachIndexed { index, key ->
+            Text(
+                if (thin && index % 2 == 1) "" else DateFormatter.bucketLabel(key, language),
+                Modifier.width(layout.slotWidth),
+                style = KvittTheme.typography.chartXLabel,
+                color = KvittTheme.colors.chartAxisLabel,
+                textAlign = TextAlign.Center,
+                maxLines = 1,
+                softWrap = false,
+                overflow = TextOverflow.Visible,
+            )
+        }
+    }
+}
+
+/** The caption under the x axis ("Vecka" in week granularity), centred under the plot. */
+@Composable
+internal fun XCaption(text: String, gutter: Dp, endGutter: Dp = 0.dp) {
+    Text(
+        text,
+        Modifier.fillMaxWidth().padding(start = gutter, end = endGutter),
+        style = KvittTheme.typography.chartXLabel,
+        color = KvittTheme.colors.chartAxisLabel,
+        textAlign = TextAlign.Center,
+    )
+}
+
 /**
  * Spending over time (design-spec §3.10): 170 dp plot, a 44 dp y gutter (wider when its labels need it, at 200 %) with gridlines at round whole-kronor values,
  * one bar per bucket (empty buckets as zero), segments stacked in [groups] order with 2 dp gaps, top corners 4 and
@@ -112,88 +219,37 @@ fun StackedBarChart(
     modifier: Modifier = Modifier,
     xCaption: String? = null,
 ) {
-    val language = kvittLanguage()
-    val typography = KvittTheme.typography
     val colors = KvittTheme.colors
-    val maxKronor = (buckets.maxOfOrNull { it.totalOre } ?: 0L) / 100
-    val step = niceStep(maxKronor)
-    val lines = if (maxKronor == 0L) 0L else ((maxKronor + step - 1) / step).coerceAtLeast(1)
-    val top = (step * lines).coerceAtLeast(1)
-    val measurer = rememberTextMeasurer()
-    val widest = (0..lines).maxOf { measurer.measure(MoneyFormatter.wholeKronor(step * it, language), typography.chartAxis).size.width }
-    val gutter = maxOf(KvittDimens.chartAxisGutter, with(LocalDensity.current) { widest.toDp() } + KvittTheme.spacing.s2)
-    val large = LocalDensity.current.fontScale >= KvittDimens.LARGE_FONT_SCALE
+    val scale = axisScale(buckets.maxOfOrNull { it.totalOre } ?: 0L)
+    val gutter = axisGutter(scale)
     Column(modifier.fillMaxWidth().semantics { contentDescription = summary }) {
         BoxWithConstraints(Modifier.fillMaxWidth()) {
-            val plotWidth = maxWidth - gutter
-            val n = buckets.size.coerceAtLeast(1)
-            val natural = (plotWidth - KvittDimens.chartBarGap * (n - 1)) / n
-            val barWidth = natural.coerceIn(KvittDimens.chartMinBar, KvittDimens.chartMaxBar)
-            val scrolls = natural < KvittDimens.chartMinBar
-            val contentWidth = if (scrolls) (barWidth + KvittDimens.chartBarGap) * n else plotWidth
+            val layout = slotLayout(buckets.size, maxWidth - gutter)
             val scroll = rememberScrollState()
-            LaunchedEffect(scrolls, buckets.size) { if (scrolls) scroll.scrollTo(scroll.maxValue) }
-            val labelHeight = with(LocalDensity.current) { typography.chartAxis.lineHeight.toDp() }
+            LaunchedEffect(layout.scrolls, buckets.size) { if (layout.scrolls) scroll.scrollTo(scroll.maxValue) }
             Row {
-                Box(Modifier.width(gutter).height(KvittDimens.chartPlot).clearAndSetSemantics { }) {
-                    for (i in 0..lines) {
-                        val fraction = if (lines == 0L) 0f else i.toFloat() / lines
-                        Text(
-                            MoneyFormatter.wholeKronor(step * i, language),
-                            Modifier
-                                .width(gutter - KvittTheme.spacing.s2)
-                                .offset(y = KvittDimens.chartPlot * (1 - fraction) - labelHeight / 2),
-                            style = typography.chartAxis,
-                            color = colors.chartAxisLabel,
-                            textAlign = TextAlign.End,
-                            maxLines = 1,
-                        )
-                    }
-                }
-                Box(Modifier.weight(1f).then(if (scrolls) Modifier.horizontalScroll(scroll) else Modifier)) {
-                    Column(Modifier.width(contentWidth)) {
-                        Box(Modifier.width(contentWidth).height(KvittDimens.chartPlot)) {
-                            Canvas(Modifier.width(contentWidth).height(KvittDimens.chartPlot).clearAndSetSemantics { }) {
-                                val stroke = KvittDimens.chartGridLine.toPx()
-                                for (i in 0..lines) {
-                                    val y = size.height * (1 - if (lines == 0L) 0f else i.toFloat() / lines)
-                                    drawLine(colors.chartGrid, Offset(0f, y.coerceIn(stroke, size.height - stroke)), Offset(size.width, y.coerceIn(stroke, size.height - stroke)), stroke)
-                                }
+                YAxisLabels(scale, gutter)
+                Box(Modifier.weight(1f).then(if (layout.scrolls) Modifier.horizontalScroll(scroll) else Modifier)) {
+                    Column(Modifier.width(layout.contentWidth)) {
+                        Box(Modifier.width(layout.contentWidth).height(KvittDimens.chartPlot)) {
+                            Canvas(Modifier.width(layout.contentWidth).height(KvittDimens.chartPlot).clearAndSetSemantics { }) {
+                                drawGridlines(scale, colors.chartGrid)
                             }
-                            Row(horizontalArrangement = Arrangement.spacedBy(if (scrolls) KvittDimens.chartBarGap else (contentWidth - barWidth * n) / (n.coerceAtLeast(2) - 1).coerceAtLeast(1))) {
+                            Row(horizontalArrangement = Arrangement.spacedBy(layout.spacing)) {
                                 buckets.forEach { bucket ->
                                     val description = barDescription(bucket)
-                                    Bar(bucket, groups, top * 100, barWidth, Modifier
+                                    Bar(bucket, groups, scale.topOre, layout.slotWidth, Modifier
                                         .clickable(role = Role.Button) { onBucket(bucket.key) }
                                         .clearAndSetSemantics { contentDescription = description; role = Role.Button })
                                 }
                             }
                         }
-                        Row(
-                            Modifier.width(contentWidth).padding(top = KvittDimens.chartXLabelTop).clearAndSetSemantics { },
-                            horizontalArrangement = Arrangement.spacedBy(if (scrolls) KvittDimens.chartBarGap else (contentWidth - barWidth * n) / (n.coerceAtLeast(2) - 1).coerceAtLeast(1)),
-                        ) {
-                            val thin = large && barWidth < KvittDimens.chartMaxBar
-                            buckets.forEachIndexed { index, bucket ->
-                                Text(
-                                    if (thin && index % 2 == 1) "" else DateFormatter.bucketLabel(bucket.key, language),
-                                    Modifier.width(barWidth),
-                                    style = typography.chartXLabel,
-                                    color = colors.chartAxisLabel,
-                                    textAlign = TextAlign.Center,
-                                    maxLines = 1,
-                                    softWrap = false,
-                                    overflow = TextOverflow.Visible,
-                                )
-                            }
-                        }
+                        XLabels(buckets.map { it.key }, layout)
                     }
                 }
             }
         }
-        if (xCaption != null) {
-            Text(xCaption, Modifier.fillMaxWidth().padding(start = gutter), style = typography.chartXLabel, color = colors.chartAxisLabel, textAlign = TextAlign.Center)
-        }
+        if (xCaption != null) XCaption(xCaption, gutter)
     }
 }
 
@@ -307,6 +363,7 @@ data class FilterToggle(val groupLabel: String, val options: List<String>, val s
 /**
  * The analytics filters (design-spec §3.10): period chip ([period] "Senaste 6 mån", TalkBack [periodSpoken]) with
  * [granularity] "Månad | Vecka"; then [measure] and [groupBy] at half width each. At ≥ 1.5× one control per row.
+ * S-12 (D-128) passes neither [measure] nor [groupBy]: the second row is left out.
  * [periodOwnRow] puts the period chip on a row of its own and the granularity toggle on the next, full width, so a long
  * custom range label ("Anpassad · 24 aug.–17 okt.") is not truncated (design frame S-11-analytics-week).
  */
@@ -316,8 +373,8 @@ fun AnalyticsFilterBar(
     periodSpoken: String,
     onPeriod: () -> Unit,
     granularity: FilterToggle,
-    measure: FilterToggle,
-    groupBy: FilterToggle,
+    measure: FilterToggle?,
+    groupBy: FilterToggle?,
     modifier: Modifier = Modifier,
     periodOwnRow: Boolean = false,
 ) {
@@ -340,28 +397,30 @@ fun AnalyticsFilterBar(
         }
     }
     val toggle: @Composable (FilterToggle, Modifier) -> Unit = { t, m -> ConnectedButtonGroup(t.options, t.selected, t.onSelect, t.groupLabel, m) }
+    val secondRow: @Composable () -> Unit = {
+        if (measure != null || groupBy != null) {
+            Row(horizontalArrangement = Arrangement.spacedBy(KvittTheme.spacing.s2)) {
+                measure?.let { toggle(it, Modifier.weight(1f)) }
+                groupBy?.let { toggle(it, Modifier.weight(1f)) }
+            }
+        }
+    }
     Column(modifier.fillMaxWidth(), verticalArrangement = Arrangement.spacedBy(KvittTheme.spacing.s3)) {
         if (large) {
             chip(Modifier)
             toggle(granularity, Modifier.fillMaxWidth())
-            toggle(measure, Modifier.fillMaxWidth())
-            toggle(groupBy, Modifier.fillMaxWidth())
+            measure?.let { toggle(it, Modifier.fillMaxWidth()) }
+            groupBy?.let { toggle(it, Modifier.fillMaxWidth()) }
         } else if (periodOwnRow) {
             chip(Modifier)
             toggle(granularity, Modifier.fillMaxWidth())
-            Row(horizontalArrangement = Arrangement.spacedBy(KvittTheme.spacing.s2)) {
-                toggle(measure, Modifier.weight(1f))
-                toggle(groupBy, Modifier.weight(1f))
-            }
+            secondRow()
         } else {
             Row(horizontalArrangement = Arrangement.spacedBy(KvittTheme.spacing.s2), verticalAlignment = Alignment.CenterVertically) {
                 chip(Modifier.weight(1f))
                 toggle(granularity, Modifier.weight(1f).width(KvittDimens.filterToggleMinWidth))
             }
-            Row(horizontalArrangement = Arrangement.spacedBy(KvittTheme.spacing.s2)) {
-                toggle(measure, Modifier.weight(1f))
-                toggle(groupBy, Modifier.weight(1f))
-            }
+            secondRow()
         }
     }
 }
diff --git a/android/core/design/src/main/kotlin/se/hagstedt/kvitt/design/chart/LineChart.kt b/android/core/design/src/main/kotlin/se/hagstedt/kvitt/design/chart/LineChart.kt
new file mode 100644
index 0000000..7656afa
--- /dev/null
+++ b/android/core/design/src/main/kotlin/se/hagstedt/kvitt/design/chart/LineChart.kt
@@ -0,0 +1,228 @@
+package se.hagstedt.kvitt.design.chart
+
+import androidx.compose.foundation.Canvas
+import androidx.compose.foundation.horizontalScroll
+import androidx.compose.foundation.layout.Arrangement
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.BoxWithConstraints
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.ExperimentalLayoutApi
+import androidx.compose.foundation.layout.FlowRow
+import androidx.compose.foundation.layout.Row
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.height
+import androidx.compose.foundation.layout.offset
+import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.layout.size
+import androidx.compose.foundation.layout.width
+import androidx.compose.foundation.rememberScrollState
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.Text
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.LaunchedEffect
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.geometry.Offset
+import androidx.compose.ui.graphics.Brush
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.graphics.Path
+import androidx.compose.ui.graphics.PathEffect
+import androidx.compose.ui.graphics.StrokeCap
+import androidx.compose.ui.graphics.StrokeJoin
+import androidx.compose.ui.graphics.drawscope.DrawScope
+import androidx.compose.ui.graphics.drawscope.Stroke
+import androidx.compose.ui.platform.LocalDensity
+import androidx.compose.ui.semantics.clearAndSetSemantics
+import androidx.compose.ui.semantics.contentDescription
+import androidx.compose.ui.semantics.semantics
+import androidx.compose.ui.text.rememberTextMeasurer
+import androidx.compose.ui.unit.Dp
+import androidx.compose.ui.unit.dp
+import se.hagstedt.kvitt.design.KvittTheme
+import se.hagstedt.kvitt.design.component.kvittLanguage
+import se.hagstedt.kvitt.design.format.MoneyFormatter
+import se.hagstedt.kvitt.design.theme.KvittDimens
+
+// The S-12 line chart of one category or account over the range (D-128), a sibling of StackedBarChart: the same plot
+// height, y gutter, gridlines, axis typography, slot geometry and horizontal scroll, drawn with Compose Canvas (D-063).
+
+/** One bucket of a line series: its key ("2026-10", "2026-W41") and its value in öre. */
+data class LinePoint(val key: String, val ore: Long)
+
+/** The three lines of [SpendLineChart], for the chart and the swatches of [LineLegend]. */
+enum class LineKind { Series, Average, MovingAverage }
+
+/** A legend entry of [LineLegend]: its [label] and which line it names. */
+data class LineLegendItem(val label: String, val kind: LineKind)
+
+/** Line chart styling (D-128): sizes and alphas of the three lines, the points and the area under the series. */
+internal object LineChartStyle {
+    val seriesWidth = 2.5.dp
+    val overlayWidth = 1.5.dp
+    val pointRadius = 3.dp
+    val dashOn = 6.dp
+    val dashOff = 4.dp
+    val swatchWidth = 16.dp
+    const val AREA_TOP_ALPHA = 0.22f
+    const val AREA_BOTTOM_ALPHA = 0.02f
+    const val AVERAGE_ALPHA = 0.75f
+    const val MOVING_ALPHA = 0.85f
+}
+
+/** The range average's colour: the group's colour, muted (D-128). */
+internal fun averageColor(color: Color): Color = color.copy(alpha = LineChartStyle.AVERAGE_ALPHA)
+
+/** The moving average's colour: the neutral axis colour, so it never reads as a second group (D-128). */
+@Composable
+internal fun movingAverageColor(): Color = KvittTheme.colors.chartAxisLabel.copy(alpha = LineChartStyle.MOVING_ALPHA)
+
+/**
+ * One group's spending over time (S-12, D-128): the plot, y gutter, gridlines and x labels of [StackedBarChart], one
+ * point per bucket (empty buckets as zero, AC-14.7) joined by a 2.5 dp line in the group's [color] with a soft fill
+ * under it; [averageOre], the range average, as a dashed line in the muted group colour labelled with its amount at the
+ * right end; [movingAverage] (one value per point) as a thinner neutral line. A range without spending shows only the 0
+ * baseline (D-068). Not interactive: TalkBack reads [summary] for the whole chart.
+ */
+@Composable
+fun SpendLineChart(
+    points: List<LinePoint>,
+    color: Color,
+    summary: String,
+    modifier: Modifier = Modifier,
+    averageOre: Long? = null,
+    movingAverage: List<Long> = emptyList(),
+    xCaption: String? = null,
+) {
+    val scale = axisScale(points.maxOfOrNull { it.ore } ?: 0L)
+    val gutter = axisGutter(scale)
+    val empty = scale.lines == 0L
+    val average = averageOre?.takeIf { it > 0 && !empty }
+    val language = kvittLanguage()
+    val typography = KvittTheme.typography
+    val averageLabel = average?.let { it to MoneyFormatter.wholeKronor((it + HALF_KRONA) / ORE_PER_KRONA, language) }
+    val measurer = rememberTextMeasurer()
+    val density = LocalDensity.current
+    val endGutter = averageLabel?.let { (_, text) -> with(density) { measurer.measure(text, typography.chartAxis).size.width.toDp() } + KvittTheme.spacing.s2 } ?: 0.dp
+    val gridColor = KvittTheme.colors.chartGrid
+    val averageLine = averageColor(color)
+    val movingLine = movingAverageColor()
+    Column(modifier.fillMaxWidth().semantics { contentDescription = summary }) {
+        BoxWithConstraints(Modifier.fillMaxWidth()) {
+            val layout = slotLayout(points.size, maxWidth - gutter - endGutter)
+            val scroll = rememberScrollState()
+            // Keyed on the gutters too: a font-scale change narrows the viewport, and the newest bucket must stay in view.
+            LaunchedEffect(layout.scrolls, points.size, gutter, endGutter) { if (layout.scrolls) scroll.scrollTo(scroll.maxValue) }
+            val centred = points.size == 1
+            Row {
+                YAxisLabels(scale, gutter)
+                Box(Modifier.weight(1f).then(if (layout.scrolls) Modifier.horizontalScroll(scroll) else Modifier)) {
+                    Column(Modifier.width(layout.contentWidth)) {
+                        Canvas(Modifier.width(layout.contentWidth).height(KvittDimens.chartPlot).clearAndSetSemantics { }) {
+                            drawGridlines(scale, gridColor)
+                            if (empty) return@Canvas
+                            val xs = points.indices.map { i -> pointX(i, centred, layout) }
+                            fun y(ore: Long) = size.height * (1 - ore.toFloat() / scale.topOre)
+                            drawArea(xs, points.map { y(it.ore) }, color)
+                            if (average != null) drawAverage(y(average), averageLine)
+                            if (movingAverage.size == points.size) drawPolyline(xs, movingAverage.map(::y), movingLine, LineChartStyle.overlayWidth.toPx())
+                            drawPolyline(xs, points.map { y(it.ore) }, color, LineChartStyle.seriesWidth.toPx())
+                            xs.forEachIndexed { i, x -> drawCircle(color, LineChartStyle.pointRadius.toPx(), Offset(x, y(points[i].ore))) }
+                        }
+                        XLabels(points.map { it.key }, layout, if (centred) Arrangement.Center else Arrangement.spacedBy(layout.spacing))
+                    }
+                }
+                averageLabel?.let { (ore, averageText) ->
+                    val labelHeight = with(density) { typography.chartAxis.lineHeight.toDp() }
+                    val y = KvittDimens.chartPlot * (1 - ore.toFloat() / scale.topOre) - labelHeight / 2
+                    Box(Modifier.width(endGutter).height(KvittDimens.chartPlot).clearAndSetSemantics { }) {
+                        Text(
+                            averageText,
+                            Modifier.padding(start = KvittTheme.spacing.s2).offset(y = y.coerceIn(0.dp, KvittDimens.chartPlot - labelHeight)),
+                            style = typography.chartAxis,
+                            color = color,
+                            maxLines = 1,
+                        )
+                    }
+                }
+            }
+        }
+        if (xCaption != null) XCaption(xCaption, gutter, endGutter)
+    }
+}
+
+private const val ORE_PER_KRONA = 100L
+private const val HALF_KRONA = 50L
+
+/** The centre of slot [i] in px (a single point sits in the middle of the plot). */
+private fun DrawScope.pointX(i: Int, centred: Boolean, layout: SlotLayout): Float =
+    if (centred) size.width / 2 else ((layout.slotWidth + layout.spacing) * i + layout.slotWidth / 2).toPx()
+
+private fun DrawScope.drawPolyline(xs: List<Float>, ys: List<Float>, color: Color, width: Float) {
+    if (xs.size < 2) return
+    val path = Path().apply {
+        moveTo(xs[0], ys[0])
+        for (i in 1 until xs.size) lineTo(xs[i], ys[i])
+    }
+    drawPath(path, color, style = Stroke(width, cap = StrokeCap.Round, join = StrokeJoin.Round))
+}
+
+/** The soft fill under the series: the group colour fading from 22 % to 2 % towards the baseline. */
+private fun DrawScope.drawArea(xs: List<Float>, ys: List<Float>, color: Color) {
+    if (xs.size < 2) return
+    val path = Path().apply {
+        moveTo(xs.first(), size.height)
+        xs.indices.forEach { lineTo(xs[it], ys[it]) }
+        lineTo(xs.last(), size.height)
+        close()
+    }
+    val brush = Brush.verticalGradient(
+        listOf(color.copy(alpha = LineChartStyle.AREA_TOP_ALPHA), color.copy(alpha = LineChartStyle.AREA_BOTTOM_ALPHA)),
+        startY = ys.min(),
+        endY = size.height,
+    )
+    drawPath(path, brush)
+}
+
+/** The range average: a dashed line across the plot (6 dp on, 4 dp off). */
+private fun DrawScope.drawAverage(y: Float, color: Color) {
+    val dash = PathEffect.dashPathEffect(floatArrayOf(LineChartStyle.dashOn.toPx(), LineChartStyle.dashOff.toPx()))
+    drawLine(color, Offset(0f, y), Offset(size.width, y), LineChartStyle.overlayWidth.toPx(), pathEffect = dash)
+}
+
+/**
+ * The legend of [SpendLineChart] (D-128): a short line swatch in each line's style (solid series, dashed average, thin
+ * neutral moving average) and its label, wrapping like [ChartLegend]; decorative for TalkBack (the summary names them).
+ */
+@OptIn(ExperimentalLayoutApi::class)
+@Composable
+fun LineLegend(items: List<LineLegendItem>, color: Color, modifier: Modifier = Modifier) {
+    val averageLine = averageColor(color)
+    val movingLine = movingAverageColor()
+    FlowRow(
+        modifier.fillMaxWidth().clearAndSetSemantics { },
+        horizontalArrangement = Arrangement.spacedBy(KvittDimens.legendItemGap),
+        verticalArrangement = Arrangement.spacedBy(KvittDimens.legendRowGap),
+    ) {
+        items.forEach { item ->
+            Row(verticalAlignment = Alignment.CenterVertically, horizontalArrangement = Arrangement.spacedBy(KvittTheme.spacing.s2)) {
+                LineSwatch(item.kind, color, averageLine, movingLine, LineChartStyle.swatchWidth)
+                Text(item.label, style = KvittTheme.typography.chartLegend, color = MaterialTheme.colorScheme.onSurfaceVariant)
+            }
+        }
+    }
+}
+
+@Composable
+private fun LineSwatch(kind: LineKind, series: Color, average: Color, moving: Color, width: Dp) {
+    Canvas(Modifier.size(width, KvittDimens.legendSwatch)) {
+        val y = size.height / 2
+        when (kind) {
+            LineKind.Series -> {
+                drawLine(series, Offset(0f, y), Offset(size.width, y), LineChartStyle.seriesWidth.toPx(), cap = StrokeCap.Round)
+                drawCircle(series, LineChartStyle.pointRadius.toPx(), Offset(size.width / 2, y))
+            }
+            LineKind.Average -> drawAverage(y, average)
+            LineKind.MovingAverage -> drawLine(moving, Offset(0f, y), Offset(size.width, y), LineChartStyle.overlayWidth.toPx(), cap = StrokeCap.Round)
+        }
+    }
+}
diff --git a/android/core/design/src/test/kotlin/se/hagstedt/kvitt/design/chart/LineChartScreenshotTest.kt b/android/core/design/src/test/kotlin/se/hagstedt/kvitt/design/chart/LineChartScreenshotTest.kt
new file mode 100644
index 0000000..18fbec8
--- /dev/null
+++ b/android/core/design/src/test/kotlin/se/hagstedt/kvitt/design/chart/LineChartScreenshotTest.kt
@@ -0,0 +1,85 @@
+package se.hagstedt.kvitt.design.chart
+
+import androidx.compose.foundation.layout.ColumnScope
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.test.junit4.v2.createComposeRule
+import org.junit.Rule
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.robolectric.ParameterizedRobolectricTestRunner
+import org.robolectric.annotation.Config
+import org.robolectric.annotation.GraphicsMode
+import se.hagstedt.kvitt.design.KvittTheme
+import se.hagstedt.kvitt.design.screenshot.Snapshots
+import se.hagstedt.kvitt.model.ColorToken
+
+/**
+ * The S-12 line chart (D-128) beside the stacked bars: six months with the range average and the moving average, a
+ * single bucket (a point, no average lines), 30 weeks that scroll to the newest, and an empty range (the 0 baseline only, D-068), × light/dark ×
+ * Swedish/English, plus 200 % for the long sheet.
+ */
+@RunWith(ParameterizedRobolectricTestRunner::class)
+@GraphicsMode(GraphicsMode.Mode.NATIVE)
+@Config(sdk = [36], qualifiers = "w411dp-h2400dp-mdpi")
+class LineChartScreenshotTest(private val sheet: String) {
+    @get:Rule
+    val compose = createComposeRule()
+
+    @Test
+    fun chart() {
+        Snapshots.snap(compose, sheet, largeFont = sheet == "line_chart_variants", content = sheets.getValue(sheet))
+    }
+
+    companion object {
+        private val months = listOf("2026-05", "2026-06", "2026-07", "2026-08", "2026-09", "2026-10")
+        private val monthly = listOf(553_515L, 563_295L, 0L, 582_855L, 892_635L, 391_000L)
+
+        // Means of the samples, as S-12 computes them (AnalyticsRules in :feature:analytics).
+        private const val MONTHLY_AVERAGE = 497_217L
+        private val monthlyMoving = listOf(553_515L, 558_405L, 372_270L, 382_050L, 491_830L, 622_163L)
+        private val weeks = (16..45).map { "2026-W$it" to (it % 5) * 41_250L + (it % 3) * 18_900L + 20_000L }
+
+        @Composable
+        private fun legend(color: Color, overlays: Boolean) = LineLegend(
+            listOfNotNull(
+                LineLegendItem("Mat & hushåll", LineKind.Series),
+                LineLegendItem("Snitt", LineKind.Average).takeIf { overlays },
+                LineLegendItem("Glidande snitt (3)", LineKind.MovingAverage).takeIf { overlays },
+            ),
+            color,
+        )
+
+        val sheets: Map<String, @Composable ColumnScope.() -> Unit> = mapOf(
+            "line_chart" to {
+                val color = KvittTheme.colors.category(ColorToken.GREEN)
+                ChartCard("Utgifter över tid") {
+                    SpendLineChart(months.zip(monthly).map { LinePoint(it.first, it.second) }, color, "", averageOre = MONTHLY_AVERAGE, movingAverage = monthlyMoving)
+                    legend(color, overlays = true)
+                }
+            },
+            "line_chart_variants" to {
+                val color = KvittTheme.colors.account(3)
+                ChartCard("En månad") {
+                    SpendLineChart(listOf(LinePoint("2026-10", 960_000)), color, "")
+                    legend(color, overlays = false)
+                }
+                ChartCard("30 veckor") {
+                    val values = weeks.map { it.second }
+                    val average = values.sum() / values.size
+                    val moving = values.indices.map { i -> values.subList((i - 2).coerceAtLeast(0), i + 1).let { w -> w.sum() / w.size } }
+                    SpendLineChart(weeks.map { LinePoint(it.first, it.second) }, color, "", averageOre = average, movingAverage = moving, xCaption = "Vecka")
+                    legend(color, overlays = true)
+                }
+                ChartCard("Tom period") {
+                    SpendLineChart(listOf("2026-11", "2026-12", "2027-01").map { LinePoint(it, 0) }, color, "")
+                    legend(color, overlays = false)
+                }
+            },
+        )
+
+        @JvmStatic
+        @ParameterizedRobolectricTestRunner.Parameters(name = "{0}")
+        fun names(): List<Array<Any>> = sheets.keys.map { arrayOf<Any>(it) }
+    }
+}
diff --git a/android/core/design/src/test/screenshots/line_chart_en_light.png b/android/core/design/src/test/screenshots/line_chart_en_light.png
new file mode 100644
index 0000000..1c47560
Binary files /dev/null and b/android/core/design/src/test/screenshots/line_chart_en_light.png differ
diff --git a/android/core/design/src/test/screenshots/line_chart_sv_dark.png b/android/core/design/src/test/screenshots/line_chart_sv_dark.png
new file mode 100644
index 0000000..b3cbab8
Binary files /dev/null and b/android/core/design/src/test/screenshots/line_chart_sv_dark.png differ
diff --git a/android/core/design/src/test/screenshots/line_chart_sv_light.png b/android/core/design/src/test/screenshots/line_chart_sv_light.png
new file mode 100644
index 0000000..56b8dc7
Binary files /dev/null and b/android/core/design/src/test/screenshots/line_chart_sv_light.png differ
diff --git a/android/core/design/src/test/screenshots/line_chart_variants_en_light.png b/android/core/design/src/test/screenshots/line_chart_variants_en_light.png
new file mode 100644
index 0000000..586e478
Binary files /dev/null and b/android/core/design/src/test/screenshots/line_chart_variants_en_light.png differ
diff --git a/android/core/design/src/test/screenshots/line_chart_variants_sv_dark.png b/android/core/design/src/test/screenshots/line_chart_variants_sv_dark.png
new file mode 100644
index 0000000..ec23770
Binary files /dev/null and b/android/core/design/src/test/screenshots/line_chart_variants_sv_dark.png differ
diff --git a/android/core/design/src/test/screenshots/line_chart_variants_sv_light.png b/android/core/design/src/test/screenshots/line_chart_variants_sv_light.png
new file mode 100644
index 0000000..ca8f469
Binary files /dev/null and b/android/core/design/src/test/screenshots/line_chart_variants_sv_light.png differ
diff --git a/android/core/design/src/test/screenshots/line_chart_variants_sv_light_200.png b/android/core/design/src/test/screenshots/line_chart_variants_sv_light_200.png
new file mode 100644
index 0000000..ec1dcbd
Binary files /dev/null and b/android/core/design/src/test/screenshots/line_chart_variants_sv_light_200.png differ
diff --git a/android/feature/analytics/src/main/kotlin/se/hagstedt/kvitt/feature/analytics/AnalyticsModel.kt b/android/feature/analytics/src/main/kotlin/se/hagstedt/kvitt/feature/analytics/AnalyticsModel.kt
index 470c2b8..dd1e247 100644
--- a/android/feature/analytics/src/main/kotlin/se/hagstedt/kvitt/feature/analytics/AnalyticsModel.kt
+++ b/android/feature/analytics/src/main/kotlin/se/hagstedt/kvitt/feature/analytics/AnalyticsModel.kt
@@ -13,6 +13,8 @@ import se.hagstedt.kvitt.model.GroupBy
 import se.hagstedt.kvitt.model.Measure
 import se.hagstedt.kvitt.model.RangePreset
 import se.hagstedt.kvitt.model.SyncSummary
+import kotlin.math.abs
+import kotlin.math.sign
 
 /** Which period control is open on S-11: none, the preset menu, or the custom range picker. */
 enum class PeriodDialog { None, Menu, CustomPicker }
@@ -32,8 +34,8 @@ sealed interface AnalyticsContent {
 /** S-11 state: the [filter] the toggles show (applied at once), the open [dialog], and the [content] (null before the first emission). */
 data class AnalyticsUiState(val filter: AnalyticsFilter, val dialog: PeriodDialog, val content: AnalyticsContent?)
 
-/** S-11 events (the ViewModel implements them; previews and screenshot tests pass their own). */
-interface AnalyticsEvents {
+/** The period and granularity events S-11 and S-12 share (D-128: S-12 has its own range and granularity). */
+interface PeriodEvents {
     fun onPeriod()
     fun onDismissPeriod()
 
@@ -43,6 +45,10 @@ interface AnalyticsEvents {
     /** The picker's "Använd": ignored unless both dates are set (§14.2.4: the editor never sends a missing date). */
     fun onCustomRange(start: String?, end: String?)
     fun onGranularity(granularity: Granularity)
+}
+
+/** S-11 events (the ViewModel implements them; previews and screenshot tests pass their own). */
+interface AnalyticsEvents : PeriodEvents {
     fun onMeasure(measure: Measure)
     fun onGroupBy(groupBy: GroupBy)
 }
@@ -96,9 +102,13 @@ data class DrillDownArgs(val filter: AnalyticsFilter, val bucketKey: String?, va
 }
 
 /**
- * S-12 state: the [args], the repository's [data] (null until it emits), the range the filter resolves to ([start],
+ * S-12 state: the [args], the repository's [data] (null until it emits), the range [filter] resolves to ([start],
  * [end], for the title of a category or account over the whole range), and the [category] or [account] behind the
  * title and header, with the account's chart position [accountIndex].
+ *
+ * A category or account over the range (D-128) has its own [filter] (range and granularity, initialised from S-11's;
+ * measure and group-by stay S-11's), its open period [dialog], and the [series] of its line chart; a bucket drill-down
+ * keeps `args.filter` and has no series.
  */
 data class DrillDownUiState(
     val args: DrillDownArgs,
@@ -108,8 +118,19 @@ data class DrillDownUiState(
     val category: Category?,
     val account: Account?,
     val accountIndex: Int,
+    val filter: AnalyticsFilter = args.filter,
+    val dialog: PeriodDialog = PeriodDialog.None,
+    val series: List<SeriesPoint>? = null,
 )
 
+/** One bucket of a group's series on S-12 (D-128): key, the bucket's dates clipped to the range, and the group's öre. */
+data class SeriesPoint(val key: String, val start: String, val end: String, val ore: Long)
+
+/** How the latest full bucket compares with the range average (D-128): "Oktober 2026: 12 % över snittet". */
+data class AverageComparison(val key: String, val percent: Long, val direction: Direction) {
+    enum class Direction { ABOVE, BELOW, ON }
+}
+
 /** The input rules of S-11 and S-12, pure so the unit tests reach them. */
 object AnalyticsRules {
     /** AC-14.2 to AC-14.5: last 6 months, month, household, category. */
@@ -137,6 +158,75 @@ object AnalyticsRules {
     /** Nothing has been synced yet: the first sync is the only loading state (SPEC §13.3). */
     fun isFirstSync(summary: SyncSummary): Boolean = summary.lastSuccessAt == null
 
+    /** D-128: the moving average on S-12 is trailing over this many buckets (the bucket and the two before it). */
+    const val MOVING_AVERAGE_WINDOW = 3
+
+    private const val PERCENT = 100L
+    private const val WEEK_LAST_DAY = 6L
+
+    /** S-12 shows its own range controls and the line chart for a category or account over the range, not for a bucket (D-128). */
+    fun isOverRange(args: DrillDownArgs): Boolean = args.bucketKey == null && (args.categoryId != null || args.accountId != null)
+
+    /** The S-11 query whose buckets carry the drill-down group's totals: grouped by account for an account, else by category. */
+    fun seriesFilter(args: DrillDownArgs, filter: AnalyticsFilter): AnalyticsFilter =
+        filter.copy(groupBy = if (args.accountId != null) GroupBy.ACCOUNT else GroupBy.CATEGORY)
+
+    /** One point per bucket of [state] for [groupId], empty buckets as zero (AC-14.7); edge buckets are clipped by `spendSeries`. */
+    fun groupSeries(state: AnalyticsState, groupId: String): List<SeriesPoint> =
+        state.buckets.map { SeriesPoint(it.key, it.start, it.end, it.totals[groupId] ?: 0L) }
+
+    /** [a] / [b] rounded half-up (away from zero at exactly half). */
+    fun divHalfUp(a: Long, b: Long): Long {
+        require(b != 0L)
+        val q = a / b
+        val r = a % b
+        return if (2 * abs(r) >= abs(b)) q + a.sign * b.sign else q
+    }
+
+    /** The range average per bucket (D-128): total ÷ number of buckets, half-up to öre; 0 for no buckets. */
+    fun rangeAverage(values: List<Long>): Long = if (values.isEmpty()) 0L else divHalfUp(values.sum(), values.size.toLong())
+
+    /** The average lines and the caption need spending in the range and at least two buckets (one bucket is its own average). */
+    fun hasAverage(values: List<Long>): Boolean = values.size > 1 && rangeAverage(values) > 0L
+
+    /**
+     * The trailing moving average (D-128): each bucket with the [window] − 1 before it, half-up to öre; the first
+     * buckets average what exists (1, then 2 buckets).
+     */
+    fun movingAverage(values: List<Long>, window: Int = MOVING_AVERAGE_WINDOW): List<Long> = values.indices.map { i ->
+        val slice = values.subList((i - window + 1).coerceAtLeast(0), i + 1)
+        divHalfUp(slice.sum(), slice.size.toLong())
+    }
+
+    /** A bucket the range does not clip: a whole calendar month (1st to last day) or a whole ISO week (7 days). */
+    fun isFullBucket(point: SeriesPoint): Boolean {
+        val start = LocalDate.parse(point.start)
+        val end = LocalDate.parse(point.end)
+        return if (point.key.contains("-W")) {
+            end.toEpochDays() - start.toEpochDays() == WEEK_LAST_DAY
+        } else {
+            start.day == 1 && LocalDate.fromEpochDays(end.toEpochDays() + 1).day == 1
+        }
+    }
+
+    /**
+     * The caption under the S-12 chart (D-128): the latest full bucket against the range average, percent of the average
+     * half-up to a whole number, "on average" when that rounds to 0. Null when [hasAverage] is false or no bucket is full.
+     */
+    fun compareWithAverage(series: List<SeriesPoint>): AverageComparison? {
+        if (!hasAverage(series.map { it.ore })) return null
+        val average = rangeAverage(series.map { it.ore })
+        val latest = series.lastOrNull(::isFullBucket) ?: return null
+        val diff = latest.ore - average
+        val percent = divHalfUp(abs(diff) * PERCENT, average)
+        val direction = when {
+            percent == 0L -> AverageComparison.Direction.ON
+            diff > 0 -> AverageComparison.Direction.ABOVE
+            else -> AverageComparison.Direction.BELOW
+        }
+        return AverageComparison(latest.key, percent, direction)
+    }
+
     /** The date picker works in UTC midnight milliseconds. */
     fun millis(isoDate: String): Long = LocalDate.parse(isoDate).toEpochDays() * MILLIS_PER_DAY
 
diff --git a/android/feature/analytics/src/main/kotlin/se/hagstedt/kvitt/feature/analytics/AnalyticsScreen.kt b/android/feature/analytics/src/main/kotlin/se/hagstedt/kvitt/feature/analytics/AnalyticsScreen.kt
index 9714704..6b6993f 100644
--- a/android/feature/analytics/src/main/kotlin/se/hagstedt/kvitt/feature/analytics/AnalyticsScreen.kt
+++ b/android/feature/analytics/src/main/kotlin/se/hagstedt/kvitt/feature/analytics/AnalyticsScreen.kt
@@ -49,6 +49,7 @@ import se.hagstedt.kvitt.design.icon.KvittIcon
 import se.hagstedt.kvitt.design.theme.KvittDimens
 import se.hagstedt.kvitt.model.Account
 import se.hagstedt.kvitt.model.AccountId
+import se.hagstedt.kvitt.model.AnalyticsFilter
 import se.hagstedt.kvitt.model.AnalyticsState
 import se.hagstedt.kvitt.model.Category
 import se.hagstedt.kvitt.model.CategoryId
@@ -127,11 +128,7 @@ private fun Filters(state: AnalyticsUiState, events: AnalyticsEvents) {
         period = period,
         periodSpoken = stringResource(R.string.analytics_period_spoken, period),
         onPeriod = events::onPeriod,
-        granularity = FilterToggle(
-            stringResource(R.string.analytics_granularity),
-            listOf(stringResource(R.string.analytics_granularity_month), stringResource(R.string.analytics_granularity_week)),
-            Granularity.entries.indexOf(filter.granularity),
-        ) { events.onGranularity(Granularity.entries[it]) },
+        granularity = granularityToggle(filter, events),
         measure = FilterToggle(
             stringResource(R.string.analytics_measure),
             listOf(stringResource(R.string.analytics_measure_household), stringResource(R.string.analytics_measure_my_share)),
@@ -147,6 +144,14 @@ private fun Filters(state: AnalyticsUiState, events: AnalyticsEvents) {
     )
 }
 
+/** "Månad | Vecka" (AC-14.3), shared by S-11 and S-12 (D-128). */
+@Composable
+internal fun granularityToggle(filter: AnalyticsFilter, events: PeriodEvents): FilterToggle = FilterToggle(
+    stringResource(R.string.analytics_granularity),
+    listOf(stringResource(R.string.analytics_granularity_month), stringResource(R.string.analytics_granularity_week)),
+    Granularity.entries.indexOf(filter.granularity),
+) { events.onGranularity(Granularity.entries[it]) }
+
 /** The range caption: "maj–okt 2026 · Hushållet", or "24 aug.–17 okt. · 8 veckor" in week granularity. */
 @Composable
 private fun totalCaption(data: AnalyticsState): String {
diff --git a/android/feature/analytics/src/main/kotlin/se/hagstedt/kvitt/feature/analytics/DrillDownScreen.kt b/android/feature/analytics/src/main/kotlin/se/hagstedt/kvitt/feature/analytics/DrillDownScreen.kt
index 3896e77..5ba9dc8 100644
--- a/android/feature/analytics/src/main/kotlin/se/hagstedt/kvitt/feature/analytics/DrillDownScreen.kt
+++ b/android/feature/analytics/src/main/kotlin/se/hagstedt/kvitt/feature/analytics/DrillDownScreen.kt
@@ -31,6 +31,13 @@ import androidx.compose.ui.text.style.TextAlign
 import androidx.hilt.lifecycle.viewmodel.compose.hiltViewModel
 import androidx.lifecycle.compose.collectAsStateWithLifecycle
 import se.hagstedt.kvitt.design.KvittTheme
+import se.hagstedt.kvitt.design.chart.AnalyticsFilterBar
+import se.hagstedt.kvitt.design.chart.ChartCard
+import se.hagstedt.kvitt.design.chart.LineKind
+import se.hagstedt.kvitt.design.chart.LineLegend
+import se.hagstedt.kvitt.design.chart.LineLegendItem
+import se.hagstedt.kvitt.design.chart.LinePoint
+import se.hagstedt.kvitt.design.chart.SpendLineChart
 import se.hagstedt.kvitt.design.component.AccountTile
 import se.hagstedt.kvitt.design.component.AmountStyle
 import se.hagstedt.kvitt.design.component.AmountTone
@@ -49,7 +56,10 @@ import se.hagstedt.kvitt.design.component.kvittLanguage
 import se.hagstedt.kvitt.design.component.spokenMoney
 import se.hagstedt.kvitt.design.icon.KvittIcon
 import se.hagstedt.kvitt.design.theme.KvittDimens
+import se.hagstedt.kvitt.model.AnalyticsFilter
 import se.hagstedt.kvitt.model.ExpenseId
+import se.hagstedt.kvitt.model.Granularity
+import se.hagstedt.kvitt.model.RangePreset
 import se.hagstedt.kvitt.core.design.R as DesignR
 
 /**
@@ -65,13 +75,18 @@ fun DrillDownScreen(
     viewModel: DrillDownViewModel = hiltViewModel(),
 ) {
     val state by viewModel.state.collectAsStateWithLifecycle()
-    DrillDownScreen(state, onOpenExpense, onBack, modifier, snackbarHostState = snackbarHostState)
+    DrillDownScreen(state, viewModel, onOpenExpense, onBack, modifier, snackbarHostState = snackbarHostState)
 }
 
-/** The stateless S-12 that previews and screenshot tests render. */
+/**
+ * The stateless S-12 that previews and screenshot tests render. A category or account over the range (D-128) shows its
+ * own period and granularity controls ([events]) above the header, and the line chart of its spending between the header
+ * and the expense rows; a bucket drill-down shows the header and the rows only.
+ */
 @Composable
 fun DrillDownScreen(
     state: DrillDownUiState,
+    events: PeriodEvents,
     onOpenExpense: (ExpenseId) -> Unit,
     onBack: () -> Unit,
     modifier: Modifier = Modifier,
@@ -94,10 +109,19 @@ fun DrillDownScreen(
             verticalArrangement = Arrangement.spacedBy(KvittTheme.spacing.detailGap),
         ) {
             val data = state.data ?: return@Column
+            val series = state.series
+            if (series != null) {
+                Box {
+                    RangeFilters(state.filter, events)
+                    if (state.dialog == PeriodDialog.Menu) PeriodMenuPopup(state.filter.preset, events)
+                }
+            }
             Header(state, title, data.totalOre, data.rows.size)
+            if (series != null) OverTimeLine(state, series)
             if (data.rows.isEmpty()) {
                 Text(
-                    stringResource(R.string.analytics_drilldown_empty),
+                    // A range with no spending reads like S-11's empty state; a bucket emptied since S-11 "Inga utgifter längre".
+                    stringResource(if (series != null) R.string.analytics_empty else R.string.analytics_drilldown_empty),
                     Modifier.fillMaxWidth().padding(KvittTheme.spacing.s4),
                     style = MaterialTheme.typography.bodyLarge,
                     color = MaterialTheme.colorScheme.onSurfaceVariant,
@@ -111,6 +135,105 @@ fun DrillDownScreen(
             }
         }
     }
+    if (state.dialog == PeriodDialog.CustomPicker && state.series != null) {
+        CustomRangeDialog(state.filter.customStart ?: state.start, state.filter.customEnd ?: state.end, events)
+    }
+}
+
+/** S-12's own period chip and "Månad | Vecka" (D-128); measure and group-by stay S-11's and are not shown. */
+@Composable
+private fun RangeFilters(filter: AnalyticsFilter, events: PeriodEvents) {
+    val period = periodLabel(filter)
+    AnalyticsFilterBar(
+        period = period,
+        periodSpoken = stringResource(R.string.analytics_period_spoken, period),
+        onPeriod = events::onPeriod,
+        granularity = granularityToggle(filter, events),
+        measure = null,
+        groupBy = null,
+        periodOwnRow = filter.preset == RangePreset.CUSTOM,
+    )
+}
+
+/**
+ * "Utgifter över tid" for one category or account (D-128): the line of its spending per bucket, the dashed range
+ * average and the trailing moving average over [AnalyticsRules.MOVING_AVERAGE_WINDOW] buckets, a legend naming the
+ * three lines, and the caption comparing the latest full bucket with the average.
+ */
+@Composable
+private fun OverTimeLine(state: DrillDownUiState, series: List<SeriesPoint>) {
+    val colors = KvittTheme.colors
+    val category = state.category
+    val color = when {
+        category != null -> colors.category(category.color)
+        state.account != null -> colors.account(state.accountIndex)
+        else -> MaterialTheme.colorScheme.primary
+    }
+    val name = category?.let { categoryName(it) } ?: state.account?.name.orEmpty()
+    val values = series.map { it.ore }
+    val average = AnalyticsRules.rangeAverage(values)
+    val withOverlays = AnalyticsRules.hasAverage(values)
+    val window = AnalyticsRules.MOVING_AVERAGE_WINDOW
+    val legend = listOfNotNull(
+        LineLegendItem(name, LineKind.Series),
+        LineLegendItem(stringResource(R.string.analytics_average), LineKind.Average).takeIf { withOverlays },
+        LineLegendItem(stringResource(R.string.analytics_moving_average, window), LineKind.MovingAverage).takeIf { withOverlays },
+    )
+    ChartCard(stringResource(R.string.analytics_over_time)) {
+        SpendLineChart(
+            points = series.map { LinePoint(it.key, it.ore) },
+            color = color,
+            summary = lineSummary(state, name, series, average),
+            averageOre = average.takeIf { withOverlays },
+            movingAverage = if (withOverlays) AnalyticsRules.movingAverage(values, window) else emptyList(),
+            xCaption = if (state.filter.granularity == Granularity.WEEK) stringResource(R.string.analytics_granularity_week) else null,
+        )
+        LineLegend(legend, color)
+        AnalyticsRules.compareWithAverage(series)?.let { comparison ->
+            Text(comparisonText(comparison), style = MaterialTheme.typography.bodySmall, color = MaterialTheme.colorScheme.onSurfaceVariant)
+        }
+    }
+}
+
+/**
+ * The chart's TalkBack summary (D-128): "Resor över tid, maj–okt 2026: från 860 kronor i maj 2026 till 9 600 kronor i
+ * oktober 2026, totalt 30 237 kronor, snitt 5 040 kronor."; one bucket: "…: totalt 9 600 kronor."
+ */
+@Composable
+private fun lineSummary(state: DrillDownUiState, name: String, series: List<SeriesPoint>, average: Long): String {
+    val start = state.start
+    val end = state.end
+    val range = if (start != null && end != null) rangeText(start, end, state.filter, LocalKvittClock.current.today, kvittLanguage(), long = true) else ""
+    val first = series.firstOrNull()
+    val last = series.lastOrNull()
+    val total = spokenMoney(series.sumOf { it.ore })
+    return if (first == null || last == null || series.size == 1) {
+        stringResource(R.string.analytics_summary_line_single, name, range, total)
+    } else {
+        stringResource(
+            R.string.analytics_summary_line,
+            name,
+            range,
+            spokenMoney(first.ore),
+            bucketName(first.key, capitalized = false),
+            spokenMoney(last.ore),
+            bucketName(last.key, capitalized = false),
+            total,
+            spokenMoney(average),
+        )
+    }
+}
+
+/** "September 2026: 12 % över snittet", "… under snittet" or "…: på snittet" (D-128). */
+@Composable
+private fun comparisonText(comparison: AverageComparison): String {
+    val bucket = bucketName(comparison.key, capitalized = true)
+    val percent = stringResource(DesignR.string.common_percent, comparison.percent.toString())
+    return when (comparison.direction) {
+        AverageComparison.Direction.ABOVE -> stringResource(R.string.analytics_vs_average_above, bucket, percent)
+        AverageComparison.Direction.BELOW -> stringResource(R.string.analytics_vs_average_below, bucket, percent)
+        AverageComparison.Direction.ON -> stringResource(R.string.analytics_vs_average_on, bucket)
+    }
 }
 
 /**
@@ -119,15 +242,14 @@ fun DrillDownScreen(
  */
 @Composable
 internal fun drillDownTitle(state: DrillDownUiState): String {
-    val args = state.args
     val name = state.category?.let { categoryName(it) } ?: state.account?.name
-    val bucket = args.bucketKey
+    val bucket = state.args.bucketKey
     val start = state.start
     val end = state.end
     return when {
         name != null && bucket != null -> stringResource(R.string.analytics_drilldown_title, name, bucketName(bucket, capitalized = false))
         name != null && start != null && end != null ->
-            stringResource(R.string.analytics_drilldown_title, name, rangeText(start, end, args.filter, LocalKvittClock.current.today, kvittLanguage()))
+            stringResource(R.string.analytics_drilldown_title, name, rangeText(start, end, state.filter, LocalKvittClock.current.today, kvittLanguage()))
         name != null -> name
         bucket != null -> bucketName(bucket, capitalized = true)
         else -> ""
diff --git a/android/feature/analytics/src/main/kotlin/se/hagstedt/kvitt/feature/analytics/DrillDownViewModel.kt b/android/feature/analytics/src/main/kotlin/se/hagstedt/kvitt/feature/analytics/DrillDownViewModel.kt
index 88ab6f8..65564e1 100644
--- a/android/feature/analytics/src/main/kotlin/se/hagstedt/kvitt/feature/analytics/DrillDownViewModel.kt
+++ b/android/feature/analytics/src/main/kotlin/se/hagstedt/kvitt/feature/analytics/DrillDownViewModel.kt
@@ -4,26 +4,42 @@ import androidx.lifecycle.SavedStateHandle
 import androidx.lifecycle.ViewModel
 import androidx.lifecycle.viewModelScope
 import dagger.hilt.android.lifecycle.HiltViewModel
+import kotlinx.coroutines.ExperimentalCoroutinesApi
+import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.SharingStarted
 import kotlinx.coroutines.flow.StateFlow
 import kotlinx.coroutines.flow.combine
+import kotlinx.coroutines.flow.flatMapLatest
 import kotlinx.coroutines.flow.stateIn
+import kotlinx.coroutines.flow.update
+import se.hagstedt.kvitt.model.Account
 import se.hagstedt.kvitt.model.AccountRepository
+import se.hagstedt.kvitt.model.AnalyticsFilter
 import se.hagstedt.kvitt.model.AnalyticsRepository
+import se.hagstedt.kvitt.model.AnalyticsState
+import se.hagstedt.kvitt.model.Category
 import se.hagstedt.kvitt.model.CategoryRepository
+import se.hagstedt.kvitt.model.DrillDownState
+import se.hagstedt.kvitt.model.Granularity
+import se.hagstedt.kvitt.model.RangePreset
 import javax.inject.Inject
 
 /**
  * S-12 (AC-14.8): the expenses behind one number of S-11. The arguments come from the navigation route
  * ([DrillDownArgs.KEYS]); the title is formatted by the screen from them, not from `DrillDownState.title` (§14.2.4).
+ *
+ * A category or account over the range (D-128) keeps its own range and granularity, starting from S-11's; changing them
+ * re-queries the total, the list and the line chart here only (S-11 keeps its own filter). The series is the group's
+ * column of S-11's own analytics query (`spendSeries`, §14.5.4), so it is computed on the phone from Room (AC-14.1).
  */
+@OptIn(ExperimentalCoroutinesApi::class)
 @HiltViewModel
 class DrillDownViewModel(
-    args: DrillDownArgs,
+    private val args: DrillDownArgs,
     analytics: AnalyticsRepository,
     categories: CategoryRepository,
     accounts: AccountRepository,
-) : ViewModel() {
+) : ViewModel(), PeriodEvents {
     @Inject
     constructor(
         savedStateHandle: SavedStateHandle,
@@ -32,25 +48,71 @@ class DrillDownViewModel(
         accounts: AccountRepository,
     ) : this(DrillDownArgs.fromArguments { savedStateHandle.get<String>(it) }, analytics, categories, accounts)
 
-    val state: StateFlow<DrillDownUiState> = combine(
-        analytics.drillDown(args.filter, args.bucketKey, args.categoryId, args.accountId),
-        analytics.analytics(args.filter),
-        categories.all(),
-        accounts.all(),
-    ) { data, range, cats, accs ->
-        val index = accs.indexOfFirst { it.id == args.accountId }
-        DrillDownUiState(
-            args = args,
-            data = data,
-            start = range.start,
-            end = range.end,
-            category = cats.firstOrNull { it.id == args.categoryId },
-            account = accs.getOrNull(index),
-            accountIndex = index.coerceAtLeast(0),
-        )
+    private val filter = MutableStateFlow(args.filter)
+    private val dialog = MutableStateFlow(PeriodDialog.None)
+
+    private val queried = filter.flatMapLatest { f ->
+        combine(
+            analytics.drillDown(f, args.bucketKey, args.categoryId, args.accountId),
+            analytics.analytics(AnalyticsRules.seriesFilter(args, f)),
+        ) { data, range -> Triple(f, data, range) }
+    }
+
+    val state: StateFlow<DrillDownUiState> = combine(queried, dialog, categories.all(), accounts.all()) { (f, data, range), d, cats, accs ->
+        drillDownUiState(args, f, d, data, range, cats, accs)
     }.stateIn(viewModelScope, SharingStarted.WhileSubscribed(STOP_TIMEOUT_MILLIS), DrillDownUiState(args, null, null, null, null, null, 0))
 
+    override fun onPeriod() = dialog.update { PeriodDialog.Menu }
+
+    override fun onDismissPeriod() = dialog.update { PeriodDialog.None }
+
+    override fun onPreset(preset: RangePreset) {
+        if (preset == RangePreset.CUSTOM) {
+            dialog.update { PeriodDialog.CustomPicker }
+        } else {
+            filter.update { AnalyticsRules.withPreset(it, preset) }
+            dialog.update { PeriodDialog.None }
+        }
+    }
+
+    override fun onCustomRange(start: String?, end: String?) {
+        val applied = AnalyticsRules.withCustomRange(filter.value, start, end) ?: return
+        filter.update { applied }
+        dialog.update { PeriodDialog.None }
+    }
+
+    override fun onGranularity(granularity: Granularity) = filter.update { it.copy(granularity = granularity) }
+
     private companion object {
         const val STOP_TIMEOUT_MILLIS = 5_000L
     }
 }
+
+/**
+ * S-12's state from one round of queries: the drill-down [data], the [range] of the current [filter] (whose buckets
+ * carry the group's series, D-128), and the categories and accounts behind the title and header.
+ */
+internal fun drillDownUiState(
+    args: DrillDownArgs,
+    filter: AnalyticsFilter,
+    dialog: PeriodDialog,
+    data: DrillDownState,
+    range: AnalyticsState,
+    categories: List<Category>,
+    accounts: List<Account>,
+): DrillDownUiState {
+    val index = accounts.indexOfFirst { it.id == args.accountId }
+    val groupId = args.categoryId?.value ?: args.accountId?.value
+    return DrillDownUiState(
+        args = args,
+        data = data,
+        start = range.start,
+        end = range.end,
+        category = categories.firstOrNull { it.id == args.categoryId },
+        account = accounts.getOrNull(index),
+        accountIndex = index.coerceAtLeast(0),
+        filter = filter,
+        dialog = dialog,
+        series = if (AnalyticsRules.isOverRange(args) && groupId != null) AnalyticsRules.groupSeries(range, groupId) else null,
+    )
+}
diff --git a/android/feature/analytics/src/main/kotlin/se/hagstedt/kvitt/feature/analytics/PeriodPicker.kt b/android/feature/analytics/src/main/kotlin/se/hagstedt/kvitt/feature/analytics/PeriodPicker.kt
index 1671481..f9fa736 100644
--- a/android/feature/analytics/src/main/kotlin/se/hagstedt/kvitt/feature/analytics/PeriodPicker.kt
+++ b/android/feature/analytics/src/main/kotlin/se/hagstedt/kvitt/feature/analytics/PeriodPicker.kt
@@ -30,7 +30,7 @@ import se.hagstedt.kvitt.model.RangePreset
 
 /** The period menu below the chip (design-spec S-11: the presets of AC-14.2, then "Anpassad…"). */
 @Composable
-internal fun PeriodMenuPopup(selected: RangePreset, events: AnalyticsEvents) {
+internal fun PeriodMenuPopup(selected: RangePreset, events: PeriodEvents) {
     val below = with(LocalDensity.current) { (KvittDimens.filterButtonMin + KvittTheme.spacing.s1).roundToPx() }
     Popup(alignment = Alignment.TopStart, offset = IntOffset(0, below), onDismissRequest = events::onDismissPeriod, properties = PopupProperties(focusable = true)) {
         PeriodMenu(selected, events::onPreset)
@@ -52,7 +52,7 @@ internal fun PeriodMenu(selected: RangePreset, onPreset: (RangePreset) -> Unit,
 }
 
 @Composable
-internal fun CustomRangeDialog(start: String?, end: String?, events: AnalyticsEvents) {
+internal fun CustomRangeDialog(start: String?, end: String?, events: PeriodEvents) {
     Dialog(onDismissRequest = events::onDismissPeriod, properties = DialogProperties(usePlatformDefaultWidth = false)) {
         CustomRangePicker(start, end, events::onCustomRange, events::onDismissPeriod)
     }
diff --git a/android/feature/analytics/src/main/res/values-sv/strings.xml b/android/feature/analytics/src/main/res/values-sv/strings.xml
index bca5a92..a012196 100644
--- a/android/feature/analytics/src/main/res/values-sv/strings.xml
+++ b/android/feature/analytics/src/main/res/values-sv/strings.xml
@@ -43,4 +43,11 @@
     <string name="analytics_measure">Mått</string>
     <string name="analytics_group_by">Gruppera efter</string>
     <string name="analytics_range_apply">Använd</string>
+    <string name="analytics_average">Snitt</string>
+    <string name="analytics_moving_average">Glidande snitt (%1$d)</string>
+    <string name="analytics_vs_average_above">%1$s: %2$s över snittet</string>
+    <string name="analytics_vs_average_below">%1$s: %2$s under snittet</string>
+    <string name="analytics_vs_average_on">%1$s: på snittet</string>
+    <string name="analytics_summary_line">%1$s över tid, %2$s: från %3$s i %4$s till %5$s i %6$s, totalt %7$s, snitt %8$s.</string>
+    <string name="analytics_summary_line_single">%1$s över tid, %2$s: totalt %3$s.</string>
 </resources>
diff --git a/android/feature/analytics/src/main/res/values/strings.xml b/android/feature/analytics/src/main/res/values/strings.xml
index fbcb492..302071a 100644
--- a/android/feature/analytics/src/main/res/values/strings.xml
+++ b/android/feature/analytics/src/main/res/values/strings.xml
@@ -43,4 +43,11 @@
     <string name="analytics_measure">Measure</string>
     <string name="analytics_group_by">Group by</string>
     <string name="analytics_range_apply">Apply</string>
+    <string name="analytics_average">Average</string>
+    <string name="analytics_moving_average">Moving average (%1$d)</string>
+    <string name="analytics_vs_average_above">%1$s: %2$s above average</string>
+    <string name="analytics_vs_average_below">%1$s: %2$s below average</string>
+    <string name="analytics_vs_average_on">%1$s: on average</string>
+    <string name="analytics_summary_line">%1$s over time, %2$s: from %3$s in %4$s to %5$s in %6$s, %7$s in total, average %8$s.</string>
+    <string name="analytics_summary_line_single">%1$s over time, %2$s: %3$s in total.</string>
 </resources>
diff --git a/android/feature/analytics/src/test/kotlin/se/hagstedt/kvitt/feature/analytics/AverageRulesTest.kt b/android/feature/analytics/src/test/kotlin/se/hagstedt/kvitt/feature/analytics/AverageRulesTest.kt
new file mode 100644
index 0000000..5d2b9d9
--- /dev/null
+++ b/android/feature/analytics/src/test/kotlin/se/hagstedt/kvitt/feature/analytics/AverageRulesTest.kt
@@ -0,0 +1,88 @@
+package se.hagstedt.kvitt.feature.analytics
+
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertFalse
+import org.junit.Assert.assertNull
+import org.junit.Assert.assertTrue
+import org.junit.Test
+import se.hagstedt.kvitt.feature.analytics.AverageComparison.Direction
+
+/** D-128: the range average, the trailing moving average over three buckets and the caption against the average. */
+class AverageRulesTest {
+    private fun month(key: String, ore: Long, start: String = "$key-01", end: String = lastDay(key)) = SeriesPoint(key, start, end, ore)
+
+    private fun lastDay(key: String): String = when (key.substringAfter('-')) {
+        "02" -> "$key-28"
+        "04", "06", "09", "11" -> "$key-30"
+        else -> "$key-31"
+    }
+
+    @Test
+    fun halfUpDivision() {
+        assertEquals(2L, AnalyticsRules.divHalfUp(3, 2))
+        assertEquals(1L, AnalyticsRules.divHalfUp(4, 3))
+        assertEquals(2L, AnalyticsRules.divHalfUp(5, 3))
+        assertEquals(-2L, AnalyticsRules.divHalfUp(-3, 2))
+        assertEquals(0L, AnalyticsRules.divHalfUp(0, 7))
+    }
+
+    @Test
+    fun rangeAverageIsTotalOverBucketsHalfUpToOre() {
+        assertEquals(100L, AnalyticsRules.rangeAverage(listOf(100, 200, 0)))
+        assertEquals(2L, AnalyticsRules.rangeAverage(listOf(1, 2)))
+        // Empty buckets count (AC-14.7): 1 000 kr over three months, one of them empty, is 333,33 kr.
+        assertEquals(33_333L, AnalyticsRules.rangeAverage(listOf(50_000, 0, 50_000)))
+        assertEquals(0L, AnalyticsRules.rangeAverage(emptyList()))
+        assertEquals(0L, AnalyticsRules.rangeAverage(listOf(0, 0, 0)))
+    }
+
+    @Test
+    fun movingAverageTrailsThreeBucketsAndShortensAtTheStart() {
+        assertEquals(3, AnalyticsRules.MOVING_AVERAGE_WINDOW)
+        assertEquals(listOf(300L, 150L, 300L, 500L, 600L), AnalyticsRules.movingAverage(listOf(300, 0, 600, 900, 300)))
+        assertEquals(listOf(1L, 2L), AnalyticsRules.movingAverage(listOf(1, 2)))
+        assertEquals(listOf(7L), AnalyticsRules.movingAverage(listOf(7)))
+        assertEquals(emptyList<Long>(), AnalyticsRules.movingAverage(emptyList()))
+        assertEquals(listOf(0L, 0L, 0L), AnalyticsRules.movingAverage(listOf(0, 0, 0)))
+    }
+
+    @Test
+    fun fullBucketsAreWholeMonthsAndWholeWeeks() {
+        assertTrue(AnalyticsRules.isFullBucket(month("2026-09", 1)))
+        assertTrue(AnalyticsRules.isFullBucket(month("2026-02", 1)))
+        assertFalse(AnalyticsRules.isFullBucket(month("2026-10", 1, end = "2026-10-17")))
+        assertFalse(AnalyticsRules.isFullBucket(month("2026-05", 1, start = "2026-05-10")))
+        assertTrue(AnalyticsRules.isFullBucket(SeriesPoint("2026-W41", "2026-10-05", "2026-10-11", 1)))
+        assertFalse(AnalyticsRules.isFullBucket(SeriesPoint("2026-W42", "2026-10-12", "2026-10-17", 1)))
+    }
+
+    @Test
+    fun captionComparesTheLatestFullBucketWithTheAverage() {
+        // Average 1 000 kr; September (full) 1 120 kr is 12 % above; October is cut off by today and skipped.
+        val series = listOf(month("2026-08", 80_000), month("2026-09", 112_000), month("2026-10", 108_000, end = "2026-10-17"))
+        assertEquals(100_000L, AnalyticsRules.rangeAverage(series.map { it.ore }))
+        assertEquals(AverageComparison("2026-09", 12, Direction.ABOVE), AnalyticsRules.compareWithAverage(series))
+    }
+
+    @Test
+    fun captionBelowAndOnAverageRoundHalfUpToWholePercent() {
+        // Average 1 000 kr; 875 kr is 12,5 % below, which rounds half-up to 13.
+        val below = listOf(month("2026-08", 112_500), month("2026-09", 87_500))
+        assertEquals(AverageComparison("2026-09", 13, Direction.BELOW), AnalyticsRules.compareWithAverage(below))
+        // Average 1 000,02 kr; 1 000,00 kr is 0,002 % below: "on average".
+        val on = listOf(month("2026-08", 100_004), month("2026-09", 100_000))
+        assertEquals(AverageComparison("2026-09", 0, Direction.ON), AnalyticsRules.compareWithAverage(on))
+    }
+
+    @Test
+    fun noCaptionWithoutAnAverageOrAFullBucket() {
+        assertNull(AnalyticsRules.compareWithAverage(listOf(month("2026-08", 0), month("2026-09", 0))))
+        assertNull(AnalyticsRules.compareWithAverage(emptyList()))
+        assertNull(AnalyticsRules.compareWithAverage(listOf(month("2026-10", 50_000, end = "2026-10-17"))))
+        // One bucket is its own average: no lines, no caption.
+        assertFalse(AnalyticsRules.hasAverage(listOf(50_000)))
+        assertNull(AnalyticsRules.compareWithAverage(listOf(month("2026-09", 50_000))))
+        assertTrue(AnalyticsRules.hasAverage(listOf(50_000, 0)))
+        assertFalse(AnalyticsRules.hasAverage(listOf(0, 0)))
+    }
+}
diff --git a/android/feature/analytics/src/test/kotlin/se/hagstedt/kvitt/feature/analytics/DrillDownViewModelTest.kt b/android/feature/analytics/src/test/kotlin/se/hagstedt/kvitt/feature/analytics/DrillDownViewModelTest.kt
index 73bcca3..a0d2319 100644
--- a/android/feature/analytics/src/test/kotlin/se/hagstedt/kvitt/feature/analytics/DrillDownViewModelTest.kt
+++ b/android/feature/analytics/src/test/kotlin/se/hagstedt/kvitt/feature/analytics/DrillDownViewModelTest.kt
@@ -4,11 +4,14 @@ import kotlinx.coroutines.ExperimentalCoroutinesApi
 import kotlinx.coroutines.flow.first
 import kotlinx.coroutines.test.runTest
 import org.junit.Assert.assertEquals
+import org.junit.Assert.assertNull
 import org.junit.Rule
 import org.junit.Test
 import se.hagstedt.kvitt.fakes.FakeRepositories
 import se.hagstedt.kvitt.fakes.analytics.AnalyticsScenarios
 import se.hagstedt.kvitt.design.testing.MainDispatcherRule
+import se.hagstedt.kvitt.model.Granularity
+import se.hagstedt.kvitt.model.RangePreset
 
 @OptIn(ExperimentalCoroutinesApi::class)
 class DrillDownViewModelTest {
@@ -39,6 +42,80 @@ class DrillDownViewModelTest {
         assertEquals(1_384_000L + 412_600L + 960_000L, state.data?.totalOre)
     }
 
+    private fun vm(args: DrillDownArgs): DrillDownViewModel {
+        val fakes = FakeRepositories(AnalyticsScenarios.loaded)
+        return DrillDownViewModel(args, fakes.analytics, fakes.categories, fakes.accounts)
+    }
+
+    /** Groceries per month of the scenario (May to September: four shops, growing by 97,80 kr a month). */
+    private fun groceries(month: Int): Long = 504_615L + 9_780L * month
+
+    @Test
+    fun categoryOverTheRangeHasOnePointPerMonth() = runTest {
+        val state = load(DrillDownArgs(AnalyticsRules.defaultFilter, null, AnalyticsScenarios.groceries.id, null))
+        val series = checkNotNull(state.series)
+        assertEquals(listOf("2026-05", "2026-06", "2026-07", "2026-08", "2026-09", "2026-10"), series.map { it.key })
+        assertEquals((5..9).map(::groceries) + 391_000L, series.map { it.ore })
+        assertEquals(state.data?.totalOre, series.sumOf { it.ore })
+    }
+
+    @Test
+    fun emptyBucketsAreZero() = runTest {
+        // Japan 2027 only has spending in September and October (AC-14.7).
+        val state = load(DrillDownArgs(AnalyticsRules.defaultFilter, null, null, AnalyticsScenarios.japan.id))
+        assertEquals(listOf(0L, 0L, 0L, 0L, 1_384_000L + 412_600L, 960_000L), state.series?.map { it.ore })
+    }
+
+    @Test
+    fun customRangeEdgeBucketsCountOnlyDatesInside() = runTest {
+        val filter = AnalyticsRules.defaultFilter.copy(preset = RangePreset.CUSTOM, customStart = "2026-05-10", customEnd = "2026-10-10")
+        val series = checkNotNull(load(DrillDownArgs(filter, null, AnalyticsScenarios.groceries.id, null)).series)
+        val may = series.first()
+        val october = series.last()
+        assertEquals("2026-05-10", may.start)
+        assertEquals((118_760L + 12_400L) + (136_510L + 9_850L) + (97_300L + 11_050L), may.ore) // 11, 19 and 25 May; not 4 May
+        assertEquals("2026-10-10", october.end)
+        assertEquals(101_245L + 78_560L, october.ore) // 1 and 7 October; not 12 or 16 October
+        assertEquals(false, AnalyticsRules.isFullBucket(may))
+        assertEquals(false, AnalyticsRules.isFullBucket(october))
+    }
+
+    @Test
+    fun ownRangeAndGranularityRequeryChartTotalAndList() = runTest {
+        val vm = vm(DrillDownArgs(AnalyticsRules.defaultFilter, null, AnalyticsScenarios.groceries.id, null))
+        vm.onGranularity(Granularity.WEEK)
+        val weeks = vm.state.first { it.series?.firstOrNull()?.key?.contains("-W") == true }
+        assertEquals(Granularity.WEEK, weeks.filter.granularity)
+        assertEquals(weeks.data?.totalOre, weeks.series?.sumOf { it.ore })
+        vm.onPreset(RangePreset.THIS_MONTH)
+        val october = vm.state.first { it.filter.preset == RangePreset.THIS_MONTH && it.data?.totalOre == 391_000L }
+        // Still weekly: October's ISO weeks up to today, 1–4, 5–11 and 12–17 October.
+        assertEquals(listOf("2026-W40", "2026-W41", "2026-W42"), october.series?.map { it.key })
+        assertEquals(listOf(101_245L, 78_560L, 86_435L + 124_760L), october.series?.map { it.ore })
+        assertEquals(4, october.data?.rows?.size)
+        // Measure and group-by stay S-11's (D-128).
+        assertEquals(AnalyticsRules.defaultFilter.measure, october.filter.measure)
+    }
+
+    @Test
+    fun customRangeOpensThePickerAndApplies() = runTest {
+        val vm = vm(DrillDownArgs(AnalyticsRules.defaultFilter, null, AnalyticsScenarios.groceries.id, null))
+        vm.onPeriod()
+        assertEquals(PeriodDialog.Menu, vm.state.first { it.dialog == PeriodDialog.Menu }.dialog)
+        vm.onPreset(RangePreset.CUSTOM)
+        vm.state.first { it.dialog == PeriodDialog.CustomPicker }
+        vm.onCustomRange("2026-09-30", "2026-08-01")
+        val applied = vm.state.first { it.filter.preset == RangePreset.CUSTOM && it.dialog == PeriodDialog.None && it.start == "2026-08-01" }
+        assertEquals(listOf("2026-08", "2026-09"), applied.series?.map { it.key })
+        assertEquals(groceries(8) + groceries(9), applied.data?.totalOre)
+    }
+
+    @Test
+    fun bucketAloneHasNoSeries() = runTest {
+        assertNull(load(DrillDownArgs(AnalyticsRules.defaultFilter, "2026-10", null, null)).series)
+        assertNull(load(DrillDownArgs(AnalyticsRules.defaultFilter, "2026-10", AnalyticsScenarios.groceries.id, null)).series)
+    }
+
     @Test
     fun bucketAloneListsEveryGroup() = runTest {
         val state = load(DrillDownArgs(AnalyticsRules.defaultFilter, "2026-10", null, null))
diff --git a/android/feature/analytics/src/test/kotlin/se/hagstedt/kvitt/feature/analytics/screenshot/DrillDownScreenshotTest.kt b/android/feature/analytics/src/test/kotlin/se/hagstedt/kvitt/feature/analytics/screenshot/DrillDownScreenshotTest.kt
index 70374eb..cb37b7d 100644
--- a/android/feature/analytics/src/test/kotlin/se/hagstedt/kvitt/feature/analytics/screenshot/DrillDownScreenshotTest.kt
+++ b/android/feature/analytics/src/test/kotlin/se/hagstedt/kvitt/feature/analytics/screenshot/DrillDownScreenshotTest.kt
@@ -17,10 +17,16 @@ import se.hagstedt.kvitt.feature.analytics.AnalyticsRules
 import se.hagstedt.kvitt.feature.analytics.DrillDownArgs
 import se.hagstedt.kvitt.feature.analytics.DrillDownScreen
 import se.hagstedt.kvitt.feature.analytics.DrillDownUiState
+import se.hagstedt.kvitt.feature.analytics.PeriodDialog
+import se.hagstedt.kvitt.feature.analytics.drillDownUiState
+import se.hagstedt.kvitt.model.AnalyticsFilter
+import se.hagstedt.kvitt.model.Granularity
+import se.hagstedt.kvitt.model.GroupBy
+import se.hagstedt.kvitt.model.Measure
 import se.hagstedt.kvitt.model.RangePreset
 import se.hagstedt.kvitt.design.testing.ScreenSnapshots
 
-/** S-12 in every state of PLAN-M7e §5, × light/dark × sv/en (plus 200 % for long content). */
+/** S-12 in every state of PLAN-M7e §5 and D-128 (the line chart in month and week, an empty range), × light/dark × sv/en (plus 200 % for long content). */
 @RunWith(ParameterizedRobolectricTestRunner::class)
 @GraphicsMode(GraphicsMode.Mode.NATIVE)
 @Config(sdk = [36], qualifiers = ScreenSnapshots.QUALIFIERS)
@@ -38,26 +44,32 @@ class DrillDownScreenshotTest(private val name: String) {
 
         private fun ui(scenario: FakeScenario, args: DrillDownArgs): DrillDownUiState = runBlocking {
             val fakes = FakeRepositories(scenario)
-            val accounts = fakes.accounts.all().first()
-            val range = fakes.analytics.analytics(args.filter).first()
-            val index = accounts.indexOfFirst { it.id == args.accountId }
-            DrillDownUiState(
+            drillDownUiState(
                 args = args,
+                filter = args.filter,
+                dialog = PeriodDialog.None,
                 data = fakes.analytics.drillDown(args.filter, args.bucketKey, args.categoryId, args.accountId).first(),
-                start = range.start,
-                end = range.end,
-                category = fakes.categories.all().first().firstOrNull { it.id == args.categoryId },
-                account = accounts.getOrNull(index),
-                accountIndex = index.coerceAtLeast(0),
+                range = fakes.analytics.analytics(AnalyticsRules.seriesFilter(args, args.filter)).first(),
+                categories = fakes.categories.all().first(),
+                accounts = fakes.accounts.all().first(),
             )
         }
 
-        private fun screen(state: DrillDownUiState): @Composable () -> Unit = { DrillDownScreen(state, {}, {}) }
+        private fun screen(state: DrillDownUiState): @Composable () -> Unit = { DrillDownScreen(state, NoEvents, {}, {}) }
+
+        /** S-12's own week range (D-128): S-11's custom weeks, the viewer's share, a category over the range. */
+        private val weekRange = AnalyticsScenarios.weekFilter.copy(groupBy = GroupBy.CATEGORY)
+
+        /** Three future months without expenses: three empty buckets, the 0 baseline only (D-068). */
+        private val emptyRange = AnalyticsFilter(RangePreset.CUSTOM, "2026-11-01", "2027-01-31", Granularity.MONTH, Measure.HOUSEHOLD, GroupBy.CATEGORY)
 
         val states: Map<String, @Composable () -> Unit> = mapOf(
             "s12_category_in_bucket" to screen(ui(AnalyticsScenarios.loaded, DrillDownArgs(defaults, "2026-10", AnalyticsScenarios.groceries.id, null))),
             "s12_bucket" to screen(ui(AnalyticsScenarios.loaded, DrillDownArgs(defaults, "2026-10", null, null))),
             "s12_category" to screen(ui(AnalyticsScenarios.loaded, DrillDownArgs(defaults, null, AnalyticsScenarios.travel.id, null))),
+            "s12_category_groceries" to screen(ui(AnalyticsScenarios.loaded, DrillDownArgs(defaults, null, AnalyticsScenarios.groceries.id, null))),
+            "s12_category_week" to screen(ui(AnalyticsScenarios.loaded, DrillDownArgs(weekRange, null, AnalyticsScenarios.groceries.id, null))),
+            "s12_category_empty_range" to screen(ui(AnalyticsScenarios.loaded, DrillDownArgs(emptyRange, null, AnalyticsScenarios.groceries.id, null))),
             "s12_account" to screen(ui(AnalyticsScenarios.loaded, DrillDownArgs(defaults, null, null, AnalyticsScenarios.japan.id))),
             "s12_account_week" to screen(ui(AnalyticsScenarios.loaded, DrillDownArgs(AnalyticsScenarios.weekFilter, "2026-W41", null, AnalyticsScenarios.vardag.id))),
             "s12_empty" to screen(ui(AnalyticsScenarios.loaded, DrillDownArgs(AnalyticsScenarios.emptyFilter, "2026-11", AnalyticsScenarios.groceries.id, null))),
diff --git a/android/feature/analytics/src/test/screenshots/s12_account_en_light.png b/android/feature/analytics/src/test/screenshots/s12_account_en_light.png
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diff --git a/android/feature/analytics/src/test/screenshots/s12_account_sv_dark.png b/android/feature/analytics/src/test/screenshots/s12_account_sv_dark.png
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diff --git a/android/feature/analytics/src/test/screenshots/s12_category_empty_range_en_light.png b/android/feature/analytics/src/test/screenshots/s12_category_empty_range_en_light.png
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diff --git a/android/feature/analytics/src/test/screenshots/s12_category_groceries_en_light.png b/android/feature/analytics/src/test/screenshots/s12_category_groceries_en_light.png
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