diff --git a/src/apps/reports/src/pages/dashboards/DashboardChart.spec.tsx b/src/apps/reports/src/pages/dashboards/DashboardChart.spec.tsx
index bc9eb3227..5d26cade2 100644
--- a/src/apps/reports/src/pages/dashboards/DashboardChart.spec.tsx
+++ b/src/apps/reports/src/pages/dashboards/DashboardChart.spec.tsx
@@ -8,21 +8,23 @@ import {
 import Highcharts from 'highcharts'
 
 import {
+    ChallengeParticipationDashboard,
     MemberPaymentByCustomerDashboard,
     NewSignupsDashboard,
 } from '../../lib/services'
 
 import { DashboardChart } from './DashboardChart'
 
+let chartOptions: Highcharts.Options
+
 jest.mock('highcharts-react-official', () => ({
     __esModule: true,
-    default: (props: {
-        options: {
-            series?: Array<{ data?: number[]; name?: string }>
-            tooltip?: { pointFormat?: string }
-        }
-    }): JSX.Element => {
-        const series = props.options.series || []
+    default: (props: { options: Highcharts.Options }): JSX.Element => {
+        chartOptions = props.options
+        const series = props.options.series as Array<{
+            data?: number[]
+            name?: string
+        }> || []
 
         return (
             <div
@@ -30,7 +32,6 @@ jest.mock('highcharts-react-official', () => ({
                 data-series-names={series.map(item => item.name)
                     .join('|')}
                 data-testid='dashboard-chart'
-                data-tooltip={props.options.tooltip?.pointFormat}
             />
         )
     },
@@ -96,10 +97,61 @@ const signupResponse: NewSignupsDashboard = {
     },
 }
 
+const challengeParticipationResponse: ChallengeParticipationDashboard = {
+    dashboard: 'challenge-participation',
+    endDate: '2026-02-01T00:00:00.000Z',
+    months: [{
+        month: '2026-01-01',
+        registrants: 120,
+        submitters: 75,
+    }],
+    startDate: '2026-01-01T00:00:00.000Z',
+    summary: {
+        peakMonth: '2026-01-01',
+        peakMonthRegistrants: 120,
+        submissionRate: 62.5,
+        totalUniqueRegistrants: 120,
+        totalUniqueSubmitters: 75,
+    },
+}
 const pointValueToken = '{point.y:,.0f}'
 const countTooltipValue = `<b>${pointValueToken}</b>`
 const currencyTooltipValue = `<b>$${pointValueToken}</b>`
 
+/**
+ * Invokes the tooltip formatter captured from the rendered chart.
+ *
+ * Tests use this helper to verify totals independently of Highcharts' DOM renderer.
+ *
+ * @param values Hovered series values for one month.
+ * @returns The formatter's tooltip HTML as one string.
+ * @throws Error when the chart has no formatter or it returns no HTML.
+ */
+function formatTooltip(values: number[]): string {
+    const formatter = chartOptions.tooltip?.formatter
+    if (!formatter) {
+        throw new Error('Tooltip formatter is missing')
+    }
+
+    const context = {
+        points: values.map(y => ({ y })),
+    } as unknown as Highcharts.TooltipFormatterContextObject
+    const tooltip = {
+        defaultFormatter: () => ['<strong>Jan ’26</strong><br/>', 'series rows'],
+    } as unknown as Highcharts.Tooltip
+    const result = formatter.call(context, tooltip)
+
+    if (typeof result === 'string') {
+        return result
+    }
+
+    if (Array.isArray(result)) {
+        return result.join('')
+    }
+
+    throw new Error('Tooltip formatter did not return HTML')
+}
+
 describe('DashboardChart', () => {
     it('formats tooltip thousands with commas', () => {
         expect(Highcharts.getOptions().lang?.thousandsSep)
@@ -126,8 +178,10 @@ describe('DashboardChart', () => {
                 'data-series-data',
                 '[[125000,140000],[80000,0],[20000,25000]]',
             )
-        expect(chart.getAttribute('data-tooltip'))
+        expect(chartOptions.tooltip?.pointFormat)
             .toContain(currencyTooltipValue)
+        expect(formatTooltip([125_000, 80_000, 20_000]))
+            .toContain('Total: <b>$225,000</b>')
         expect(within(table)
             .getByRole('columnheader', { name: 'Customer A' }))
             .toBeInTheDocument()
@@ -142,20 +196,30 @@ describe('DashboardChart', () => {
             .toBeInTheDocument()
     })
 
-    it('keeps existing count dashboards unit-free', () => {
+    it('keeps count dashboard tooltips unit-free and adds their total', () => {
         render(<DashboardChart response={signupResponse} />)
 
-        const chart = screen.getByTestId('dashboard-chart')
         const table = screen.getByRole('table', {
             name: 'New Signups by Month monthly data',
         })
 
-        expect(chart.getAttribute('data-tooltip'))
+        expect(chartOptions.tooltip?.pointFormat)
             .toContain(countTooltipValue)
-        expect(chart.getAttribute('data-tooltip'))
+        expect(chartOptions.tooltip?.pointFormat)
             .not.toContain(currencyTooltipValue)
+        expect(formatTooltip([90, 10]))
+            .toContain('Total: <b>100</b>')
+        expect(formatTooltip([90, 10]))
+            .not.toContain('$100')
         expect(within(table)
             .getByRole('cell', { name: '90' }))
             .toBeInTheDocument()
     })
+
+    it('adds a total to grouped report tooltips', () => {
+        render(<DashboardChart response={challengeParticipationResponse} />)
+
+        expect(formatTooltip([120, 75]))
+            .toContain('Total: <b>195</b>')
+    })
 })
diff --git a/src/apps/reports/src/pages/dashboards/DashboardChart.tsx b/src/apps/reports/src/pages/dashboards/DashboardChart.tsx
index 54182e43a..eeeab09db 100644
--- a/src/apps/reports/src/pages/dashboards/DashboardChart.tsx
+++ b/src/apps/reports/src/pages/dashboards/DashboardChart.tsx
@@ -50,7 +50,7 @@ function getSeriesValue(month: DashboardMonth, key: string): number {
  *
  * @param props Dashboard response and compact-card presentation flag.
  * @returns A stacked or grouped column chart with month categories along the
- * bottom axis and an accessible monthly data table.
+ * bottom axis, monthly tooltip totals, and an accessible monthly data table.
  * @throws Does not throw. Invalid or absent point values are rendered as zero.
  */
 export const DashboardChart: FC<DashboardChartProps> = props => {
@@ -119,6 +119,29 @@ export const DashboardChart: FC<DashboardChartProps> = props => {
             text: undefined,
         },
         tooltip: {
+            /**
+             * Appends the hovered month's total to Highcharts' shared tooltip.
+             *
+             * Highcharts invokes this callback for card and detail charts.
+             *
+             * @param tooltip Highcharts tooltip used to render the existing rows.
+             * @returns The default tooltip content followed by the formatted total.
+             * @throws Does not throw for the normalized chart-series values.
+             */
+            formatter(tooltip: Highcharts.Tooltip) {
+                // Highcharts supplies the shared tooltip context through `this`.
+                // eslint-disable-next-line react/no-this-in-sfc
+                const points = this.points || [this]
+                const total = points.reduce((sum, point) => sum + (point.y ?? 0), 0)
+                // eslint-disable-next-line react/no-this-in-sfc
+                const content = tooltip.defaultFormatter.call(this, tooltip)
+                const totalRow = `Total: <b>${isCurrency ? '$' : ''}`
+                    + `${Highcharts.numberFormat(total, 0)}</b>`
+
+                return Array.isArray(content)
+                    ? [...content, totalRow]
+                    : `${content}${totalRow}`
+            },
             headerFormat: '<strong>{point.key}</strong><br/>',
             pointFormat: '<span style="color:{series.color}">●</span> '
                 + `{series.name}: <b>${isCurrency ? '$' : ''}{point.y:,.0f}</b><br/>`,