diff --git a/public/app/features/alerting/unified/components/rule-viewer/RuleViewer.test.tsx b/public/app/features/alerting/unified/components/rule-viewer/RuleViewer.test.tsx
index ed59a8e9791..992eba0a1a2 100644
--- a/public/app/features/alerting/unified/components/rule-viewer/RuleViewer.test.tsx
+++ b/public/app/features/alerting/unified/components/rule-viewer/RuleViewer.test.tsx
@@ -12,18 +12,21 @@ import { CombinedRule, RuleIdentifier } from 'app/types/unified-alerting';
 import {
   getCloudRule,
   getGrafanaRule,
+  getVanillaPromRule,
   grantUserPermissions,
   mockDataSource,
   mockPluginLinkExtension,
+  mockPromAlertingRule,
 } from '../../mocks';
 import { grafanaRulerRule } from '../../mocks/grafanaRulerApi';
 import { setupDataSources } from '../../testSetup/datasources';
 import { Annotation } from '../../utils/constants';
 import { DataSourceType } from '../../utils/datasource';
 import * as ruleId from '../../utils/rule-id';
+import { stringifyIdentifier } from '../../utils/rule-id';
 
 import { AlertRuleProvider } from './RuleContext';
-import RuleViewer from './RuleViewer';
+import RuleViewer, { ActiveTab } from './RuleViewer';
 
 // metadata and interactive elements
 const ELEMENTS = {
@@ -35,6 +38,12 @@ const ELEMENTS = {
     evaluationInterval: (interval: string) => byText(`Every ${interval}`),
     label: ([key, value]: [string, string]) => byRole('listitem', { name: `${key}: ${value}` }),
   },
+  details: {
+    pendingPeriod: byText(/Pending period/i),
+  },
+  tabs: {
+    details: byRole('tab', { name: /Details/i }),
+  },
   actions: {
     edit: byRole('link', { name: 'Edit' }),
     more: {
@@ -259,13 +268,39 @@ describe('RuleViewer', () => {
       await waitFor(() => expect(ELEMENTS.actions.more.pluginActions.declareIncident.get()).toBeEnabled());
     });
   });
+
+  describe('Vanilla Prometheus rule', () => {
+    const mockRule = getVanillaPromRule({
+      name: 'prom test alert',
+      annotations: { [Annotation.summary]: 'prom summary', [Annotation.runbookURL]: 'https://runbook.example.com' },
+      promRule: {
+        ...mockPromAlertingRule(),
+        duration: 900, // 15 minutes
+      },
+    });
+
+    const mockRuleIdentifier = ruleId.fromCombinedRule('prometheus', mockRule);
+
+    it('should render pending period for vanilla Prometheus alert rule', async () => {
+      renderRuleViewer(mockRule, mockRuleIdentifier, ActiveTab.Details);
+
+      expect(screen.getByText('prom test alert')).toBeInTheDocument();
+
+      // One summary is rendered by the Title component, and the other by the DetailsTab component
+      expect(ELEMENTS.metadata.summary(mockRule.annotations[Annotation.summary]).getAll()).toHaveLength(2);
+
+      expect(within(ELEMENTS.details.pendingPeriod.get()).getByText(/15m/i)).toBeInTheDocument();
+    });
+  });
 });
 
-const renderRuleViewer = async (rule: CombinedRule, identifier: RuleIdentifier) => {
+const renderRuleViewer = async (rule: CombinedRule, identifier: RuleIdentifier, tab: ActiveTab = ActiveTab.Query) => {
+  const path = `/alerting/${identifier.ruleSourceName}/${stringifyIdentifier(identifier)}/view?tab=${tab}`;
   render(
     <AlertRuleProvider identifier={identifier} rule={rule}>
       <RuleViewer />
-    </AlertRuleProvider>
+    </AlertRuleProvider>,
+    { historyOptions: { initialEntries: [path] } }
   );
 
   await waitFor(() => expect(ELEMENTS.loading.query()).not.toBeInTheDocument());
diff --git a/public/app/features/alerting/unified/components/rule-viewer/tabs/Details.tsx b/public/app/features/alerting/unified/components/rule-viewer/tabs/Details.tsx
index 5c723326abb..53c74196586 100644
--- a/public/app/features/alerting/unified/components/rule-viewer/tabs/Details.tsx
+++ b/public/app/features/alerting/unified/components/rule-viewer/tabs/Details.tsx
@@ -7,6 +7,7 @@ import { ClipboardButton, Stack, Text, TextLink, useStyles2 } from '@grafana/ui'
 import { CombinedRule } from 'app/types/unified-alerting';
 import { Annotations } from 'app/types/unified-alerting-dto';
 
+import { usePendingPeriod } from '../../../hooks/rules/usePendingPeriod';
 import { isGrafanaRulerRule, isRecordingRulerRule } from '../../../utils/rules';
 import { MetaText } from '../../MetaText';
 import { Tokenize } from '../../Tokenize';
@@ -26,6 +27,8 @@ const Details = ({ rule }: DetailsProps) => {
 
   let ruleType: RuleType;
 
+  const pendingPeriod = usePendingPeriod(rule);
+
   if (isGrafanaRulerRule(rule.rulerRule)) {
     ruleType = RuleType.GrafanaManagedAlertRule;
   } else if (isRecordingRulerRule(rule.rulerRule)) {
@@ -89,10 +92,10 @@ const Details = ({ rule }: DetailsProps) => {
           )}
         </MetaText>
         <MetaText direction="column">
-          {!isRecordingRulerRule(rule.rulerRule) && (
+          {pendingPeriod && (
             <>
               Pending period
-              <Text color="primary">{rule.rulerRule?.for ?? '0s'}</Text>
+              <Text color="primary">{pendingPeriod}</Text>
             </>
           )}
         </MetaText>
diff --git a/public/app/features/alerting/unified/components/rules/RuleDetails.tsx b/public/app/features/alerting/unified/components/rules/RuleDetails.tsx
index 6c8ddb552e1..7c7659a5e32 100644
--- a/public/app/features/alerting/unified/components/rules/RuleDetails.tsx
+++ b/public/app/features/alerting/unified/components/rules/RuleDetails.tsx
@@ -5,8 +5,9 @@ import { Tooltip, useStyles2 } from '@grafana/ui';
 import { Time } from 'app/features/explore/Time';
 import { CombinedRule } from 'app/types/unified-alerting';
 
+import { usePendingPeriod } from '../../hooks/rules/usePendingPeriod';
 import { useCleanAnnotations } from '../../utils/annotations';
-import { isGrafanaRecordingRule, isRecordingRulerRule } from '../../utils/rules';
+import { isGrafanaRecordingRule } from '../../utils/rules';
 import { isNullDate } from '../../utils/time';
 import { AlertLabels } from '../AlertLabels';
 import { DetailsField } from '../DetailsField';
@@ -64,16 +65,12 @@ interface EvaluationBehaviorSummaryProps {
 }
 
 const EvaluationBehaviorSummary = ({ rule }: EvaluationBehaviorSummaryProps) => {
-  let forDuration: string | undefined;
   const every = rule.group.interval;
   const lastEvaluation = rule.promRule?.lastEvaluation;
   const lastEvaluationDuration = rule.promRule?.evaluationTime;
   const metric = isGrafanaRecordingRule(rule.rulerRule) ? rule.rulerRule?.grafana_alert.record?.metric : undefined;
 
-  // recording rules don't have a for duration
-  if (!isRecordingRulerRule(rule.rulerRule)) {
-    forDuration = rule.rulerRule?.for ?? '0s';
-  }
+  const pendingPeriod = usePendingPeriod(rule);
 
   return (
     <>
@@ -88,9 +85,11 @@ const EvaluationBehaviorSummary = ({ rule }: EvaluationBehaviorSummaryProps) =>
         </DetailsField>
       )}
 
-      <DetailsField label="Pending period" horizontal={true}>
-        {forDuration}
-      </DetailsField>
+      {pendingPeriod && (
+        <DetailsField label="Pending period" horizontal={true}>
+          {pendingPeriod}
+        </DetailsField>
+      )}
 
       {lastEvaluation && !isNullDate(lastEvaluation) && (
         <DetailsField label="Last evaluation" horizontal={true}>
diff --git a/public/app/features/alerting/unified/hooks/rules/usePendingPeriod.tsx b/public/app/features/alerting/unified/hooks/rules/usePendingPeriod.tsx
new file mode 100644
index 00000000000..d7ebd337f7c
--- /dev/null
+++ b/public/app/features/alerting/unified/hooks/rules/usePendingPeriod.tsx
@@ -0,0 +1,9 @@
+import { useMemo } from 'react';
+
+import { CombinedRule } from 'app/types/unified-alerting';
+
+import { getPendingPeriod } from '../../utils/rules';
+
+export function usePendingPeriod(rule: CombinedRule): string | undefined {
+  return useMemo(() => getPendingPeriod(rule), [rule]);
+}
diff --git a/public/app/features/alerting/unified/mocks.ts b/public/app/features/alerting/unified/mocks.ts
index 699252137db..632868a90e0 100644
--- a/public/app/features/alerting/unified/mocks.ts
+++ b/public/app/features/alerting/unified/mocks.ts
@@ -785,6 +785,19 @@ export function getCloudRule(override?: Partial<CombinedRule>) {
   });
 }
 
+export function getVanillaPromRule(override?: Partial<Omit<CombinedRule, 'rulerRule'>>) {
+  return mockCombinedRule({
+    namespace: {
+      groups: [],
+      name: 'Prometheus',
+      rulesSource: mockDataSource(),
+    },
+    promRule: mockPromAlertingRule(),
+    rulerRule: undefined,
+    ...override,
+  });
+}
+
 export function mockPluginLinkExtension(extension: Partial<PluginExtensionLink>): PluginExtensionLink {
   return {
     type: PluginExtensionTypes.link,
diff --git a/public/app/features/alerting/unified/utils/rules.ts b/public/app/features/alerting/unified/utils/rules.ts
index fe4aa16b4b4..cc4a7af1af9 100644
--- a/public/app/features/alerting/unified/utils/rules.ts
+++ b/public/app/features/alerting/unified/utils/rules.ts
@@ -44,7 +44,7 @@ import { RULER_NOT_SUPPORTED_MSG } from './constants';
 import { getRulesSourceName, isGrafanaRulesSource } from './datasource';
 import { GRAFANA_ORIGIN_LABEL } from './labels';
 import { AsyncRequestState } from './redux';
-import { safeParsePrometheusDuration } from './time';
+import { formatPrometheusDuration, safeParsePrometheusDuration } from './time';
 
 export function isAlertingRule(rule: Rule | undefined): rule is AlertingRule {
   return typeof rule === 'object' && rule.type === PromRuleType.Alerting;
@@ -137,6 +137,26 @@ export function getRuleHealth(health: string): RuleHealth | undefined {
   }
 }
 
+export function getPendingPeriod(rule: CombinedRule): string | undefined {
+  if (isRecordingRulerRule(rule.rulerRule) || isRecordingRule(rule.promRule)) {
+    return undefined;
+  }
+
+  // We prefer the for duration from the ruler rule because it is formatted as a duration string
+  // Prometheus duration is in seconds and we need to format it as a duration string
+  // Additionally, due to eventual consistency of the Prometheus endpoint the ruler data might be newer
+  if (isAlertingRulerRule(rule.rulerRule)) {
+    return rule.rulerRule.for;
+  }
+
+  if (isAlertingRule(rule.promRule)) {
+    const durationInMilliseconds = (rule.promRule.duration ?? 0) * 1000;
+    return formatPrometheusDuration(durationInMilliseconds);
+  }
+
+  return undefined;
+}
+
 export interface RulePluginOrigin {
   pluginId: string;
 }
diff --git a/public/app/types/unified-alerting.ts b/public/app/types/unified-alerting.ts
index 338fa189fc9..734e6c650ad 100644
--- a/public/app/types/unified-alerting.ts
+++ b/public/app/types/unified-alerting.ts
@@ -50,6 +50,11 @@ export interface AlertingRule extends RuleBase {
   };
   state: PromAlertingRuleState;
   type: PromRuleType.Alerting;
+
+  /**
+   * Pending period in seconds, aka for. 0 or undefined means no pending period
+   */
+  duration?: number;
   totals?: Partial<Record<Lowercase<GrafanaAlertState>, number>>;
   totalsFiltered?: Partial<Record<Lowercase<GrafanaAlertState>, number>>;
   activeAt?: string; // ISO timestamp