diff --git a/packages/frontend/src/pages/Inbox/Inbox.tsx b/packages/frontend/src/pages/Inbox/Inbox.tsx
index c14698ad..f7d29fbd 100644
--- a/packages/frontend/src/pages/Inbox/Inbox.tsx
+++ b/packages/frontend/src/pages/Inbox/Inbox.tsx
@@ -112,7 +112,11 @@ export const Inbox = ({ viewType }: InboxProps) => {
       </section>
       <Section spacing={3} margin="section">
         {dataSourceSuccess && !filteredItems.length && <h1>{t(`inbox.heading.title.${viewType}`, { count: 0 })}</h1>}
-        <DialogList items={mappedGroupedDialogs} groups={groups} sortGroupBy={(a, b) => b[0].localeCompare(a[0])} />
+        <DialogList
+          items={mappedGroupedDialogs}
+          groups={groups}
+          sortGroupBy={([aKey], [bKey]) => (groups[bKey]?.orderIndex ?? 0) - (groups[aKey]?.orderIndex ?? 0)}
+        />
       </Section>
     </>
   );
diff --git a/packages/frontend/src/pages/Inbox/useGroupedDialogs.spec.tsx b/packages/frontend/src/pages/Inbox/useGroupedDialogs.spec.tsx
new file mode 100644
index 00000000..f6ba8826
--- /dev/null
+++ b/packages/frontend/src/pages/Inbox/useGroupedDialogs.spec.tsx
@@ -0,0 +1,250 @@
+import { renderHook } from '@testing-library/react';
+import type { DialogStatus, SystemLabel } from 'bff-types-generated';
+import { useTranslation } from 'react-i18next';
+import { type Mock, beforeEach, describe, expect, it, vi } from 'vitest';
+import type { InboxViewType } from '../../api/useDialogs.tsx';
+import { useFormat } from '../../i18n/useDateFnsLocale.tsx';
+import useGroupedDialogs from './useGroupedDialogs.tsx';
+
+vi.mock('react-i18next', () => ({
+  useTranslation: vi.fn(),
+}));
+
+vi.mock('../../i18n/useDateFnsLocale.tsx', () => ({
+  useFormat: vi.fn(),
+}));
+
+const mockData = [
+  {
+    id: '01953842-438a-7232-b9c0-d90bd89e1072',
+    party: 'urn:altinn:person:identifier-no:14886498226',
+    title: 'Dialog laget med Scenario Builder 2025-2-24 14:52',
+    summary: 'Denne teksten representerer et sammendrag av dialogen, som er opprettet av serviceOwner i dialogporten.',
+    sender: {
+      name: 'Digitaliseringsdirektoratet',
+      isCompany: true,
+      imageURL: '',
+    },
+    receiver: {
+      name: 'Hjelpelinje Ordinær',
+      isCompany: false,
+    },
+    guiAttachmentCount: 0,
+    createdAt: '2025-02-24T14:00:21.642Z',
+    updatedAt: '2025-02-24T14:02:58.540Z',
+    status: 'NEW' as DialogStatus,
+    isSeenByEndUser: true,
+    label: 'DEFAULT' as SystemLabel,
+    org: 'digdir',
+    seenByLabel: 'Sett av deg',
+    seenByOthersCount: 0,
+    viewType: 'inbox' as InboxViewType,
+  },
+  {
+    id: '0195383e-0d9a-73b1-b96b-73c49e31097d',
+    party: 'urn:altinn:person:identifier-no:14886498226',
+    title: 'Dialog laget med Scenario Builder 2025-2-24 14:52',
+    summary: 'Denne teksten representerer et sammendrag av dialogen, som er opprettet av serviceOwner i dialogporten.',
+    sender: {
+      name: 'Digitaliseringsdirektoratet',
+      isCompany: true,
+      imageURL: '',
+    },
+    receiver: {
+      name: 'Hjelpelinje Ordinær',
+      isCompany: false,
+    },
+    guiAttachmentCount: 1,
+    createdAt: '2025-02-24T13:55:45.689Z',
+    updatedAt: '2025-02-24T13:55:45.689Z',
+    status: 'NEW' as DialogStatus,
+    isSeenByEndUser: true,
+    label: 'DEFAULT' as SystemLabel,
+    org: 'digdir',
+    seenByLabel: 'Sett av deg',
+    seenByOthersCount: 0,
+    viewType: 'inbox' as InboxViewType,
+  },
+  {
+    id: '0195383b-6068-726a-b632-1ff3cc836e9a',
+    party: 'urn:altinn:person:identifier-no:14886498226',
+    title: 'Dialog laget med Scenario Builder 2025-2-24 14:52',
+    summary: 'Denne teksten representerer et sammendrag av dialogen, som er opprettet av serviceOwner i dialogporten.',
+    sender: {
+      name: 'Digitaliseringsdirektoratet',
+      isCompany: true,
+      imageURL: '',
+    },
+    receiver: {
+      name: 'Hjelpelinje Ordinær',
+      isCompany: false,
+    },
+    guiAttachmentCount: 1,
+    createdAt: '2025-02-24T13:52:50.280Z',
+    updatedAt: '2025-02-24T13:52:50.280Z',
+    status: 'NEW' as DialogStatus,
+    isSeenByEndUser: true,
+    label: 'DEFAULT' as SystemLabel,
+    org: 'digdir',
+    seenByLabel: 'Sett av deg',
+    seenByOthersCount: 0,
+    viewType: 'inbox' as InboxViewType,
+  },
+  {
+    id: '01937766-ff24-7305-9361-d14743d2db30',
+    party: 'urn:altinn:person:identifier-no:14886498226',
+    title: 'Test melding8',
+    summary: 'Et sammendrag her. Maks 200 tegn, ingen HTML-støtte. Påkrevd. Vises i liste.',
+    sender: {
+      name: 'digitaliseringsdirektoratet',
+      isCompany: true,
+      imageURL: '',
+    },
+    receiver: {
+      name: 'Hjelpelinje Ordinær',
+      isCompany: false,
+    },
+    guiAttachmentCount: 1,
+    createdAt: '2024-11-29T10:10:58.980Z',
+    updatedAt: '2024-11-29T10:10:58.980Z',
+    status: 'NEW' as DialogStatus,
+    isSeenByEndUser: true,
+    label: 'DEFAULT' as SystemLabel,
+    org: 'digitaliseringsdirektoratet',
+    seenByLabel: 'Sett av deg',
+    seenByOthersCount: 0,
+    viewType: 'inbox' as InboxViewType,
+  },
+  {
+    id: '01936e30-ac82-70f3-96ba-eb3ccd31586a',
+    party: 'urn:altinn:person:identifier-no:14886498226',
+    title: 'Test melding3',
+    summary: 'Et sammendrag her. Maks 200 tegn, ingen HTML-støtte. Påkrevd. Vises i liste.',
+    sender: {
+      name: 'digitaliseringsdirektoratet',
+      isCompany: true,
+      imageURL: '',
+    },
+    receiver: {
+      name: 'Hjelpelinje Ordinær',
+      isCompany: false,
+    },
+    guiAttachmentCount: 1,
+    createdAt: '2024-11-27T15:15:03.934Z',
+    updatedAt: '2024-11-27T15:15:03.934Z',
+    status: 'NEW' as DialogStatus,
+    isSeenByEndUser: true,
+    label: 'DEFAULT' as SystemLabel,
+    org: 'digitaliseringsdirektoratet',
+    seenByLabel: 'Sett av deg',
+    seenByOthersCount: 0,
+    viewType: 'inbox' as InboxViewType,
+  },
+  {
+    id: 'f67d9101-5149-6377-95db-6146e6b2e196',
+    party: 'urn:altinn:person:identifier-no:14886498226',
+    title: 'Tjeneste for rapportering av et eller annet fra SKE',
+    summary: 'Et sammendrag her. Maks 200 tegn, ingen riktekst-støtte. Påkrevd. Vises i liste.',
+    sender: {
+      name: 'Skatteetaten',
+      isCompany: true,
+      imageURL: 'https://altinncdn.no/orgs/skd/skd.png',
+    },
+    receiver: {
+      name: 'Hjelpelinje Ordinær',
+      isCompany: false,
+    },
+    guiAttachmentCount: 2,
+    createdAt: '2024-08-23T06:39:38.321Z',
+    updatedAt: '2024-08-23T06:39:38.321Z',
+    status: 'NEW' as DialogStatus,
+    isSeenByEndUser: true,
+    label: 'DEFAULT' as SystemLabel,
+    org: 'skd',
+    seenByLabel: 'Sett av deg',
+    seenByOthersCount: 0,
+    viewType: 'inbox' as InboxViewType,
+  },
+  {
+    id: 'f57d9101-e17a-8b76-94ba-c6d63f56b96f',
+    party: 'urn:altinn:person:identifier-no:14886498226',
+    title: 'Tjeneste for rapportering av et eller annet fra SKE',
+    summary: 'Et sammendrag her. Maks 200 tegn, ingen riktekst-støtte. Påkrevd. Vises i liste.',
+    sender: {
+      name: 'Skatteetaten',
+      isCompany: true,
+      imageURL: 'https://altinncdn.no/orgs/skd/skd.png',
+    },
+    receiver: {
+      name: 'Hjelpelinje Ordinær',
+      isCompany: false,
+    },
+    guiAttachmentCount: 2,
+    createdAt: '2024-08-23T06:38:45.473Z',
+    updatedAt: '2024-08-23T06:38:45.473Z',
+    status: 'NEW' as DialogStatus,
+    isSeenByEndUser: true,
+    label: 'DEFAULT' as SystemLabel,
+    org: 'skd',
+    seenByLabel: 'Sett av deg',
+    seenByOthersCount: 0,
+    viewType: 'inbox' as InboxViewType,
+  },
+];
+
+describe('useGroupedDialogs', () => {
+  const t = vi.fn((key) => key);
+  const format = vi.fn((date) => date.toString());
+
+  beforeEach(() => {
+    (useTranslation as Mock).mockReturnValue({ t });
+    (useFormat as Mock).mockReturnValue(format);
+  });
+
+  it('should return loading items when isLoading is true', () => {
+    const { result } = renderHook(() =>
+      useGroupedDialogs({
+        items: [],
+        displaySearchResults: false,
+        viewType: 'inbox',
+        isLoading: true,
+      }),
+    );
+
+    expect(result.current.mappedGroupedDialogs).toHaveLength(5);
+    expect(result.current.groups).toEqual({ loading: { title: 'word.loading' } });
+  });
+
+  it('should return grouped dialogs when isLoading is false', () => {
+    const { result } = renderHook(() =>
+      useGroupedDialogs({
+        items: mockData,
+        displaySearchResults: true,
+        viewType: 'inbox',
+        isLoading: false,
+      }),
+    );
+
+    expect(result.current.mappedGroupedDialogs).toHaveLength(7);
+    expect(result.current.groups).toEqual({
+      inbox: { title: 'inbox.heading.search_results.inbox', orderIndex: null },
+    });
+  });
+
+  it('should generat groups orderIndex correctly', () => {
+    const { result } = renderHook(() =>
+      useGroupedDialogs({
+        items: mockData,
+        displaySearchResults: false,
+        viewType: 'inbox',
+        isLoading: false,
+      }),
+    );
+
+    const groups = result.current.groups;
+    const uniqueOrderIndexes = [...new Set(Object.values(groups).map((item) => item.orderIndex?.toString()))];
+
+    expect(uniqueOrderIndexes).toHaveLength(2);
+    expect(uniqueOrderIndexes.toString()).toBe('2025,2024');
+  });
+});
diff --git a/packages/frontend/src/pages/Inbox/useGroupedDialogs.tsx b/packages/frontend/src/pages/Inbox/useGroupedDialogs.tsx
index 3feaa496..8dfef06b 100644
--- a/packages/frontend/src/pages/Inbox/useGroupedDialogs.tsx
+++ b/packages/frontend/src/pages/Inbox/useGroupedDialogs.tsx
@@ -16,16 +16,21 @@ interface GroupedItem {
   id: string | number;
   label: string;
   items: InboxItemInput[];
+  orderIndex: number | null;
+}
+
+interface DialogListGroupPropsSort extends DialogListGroupProps {
+  orderIndex?: number | null;
 }
 
 interface UseGroupedDialogsOutput {
   mappedGroupedDialogs: DialogListItemProps[];
-  groups?: Record<string, DialogListGroupProps>;
+  groups: Record<string, DialogListGroupPropsSort>;
 }
 
 interface UseGroupedDialogsProps {
   items: InboxItemInput[];
-  filters: FilterState;
+  filters?: FilterState;
   displaySearchResults: boolean;
   viewType: InboxViewType;
   isLoading: boolean;
@@ -132,15 +137,25 @@ const useGroupedDialogs = ({
       };
     }
 
+    const getOrderIndex = (createdAt: Date, isDateKey: boolean) => {
+      if (!isDateKey) return null;
+
+      if (allWithinSameYear) {
+        return createdAt.getMonth();
+      }
+      return createdAt.getFullYear();
+    };
+
     const groupedItems = items.reduce<GroupedItem[]>((acc, item, _, list) => {
       const createdAt = new Date(item.createdAt);
-
       const groupKey = displaySearchResults
         ? item.viewType
         : allWithinSameYear
           ? format(createdAt, 'LLLL')
           : format(createdAt, 'yyyy');
 
+      const isDateKey = !displaySearchResults;
+
       const label = displaySearchResults
         ? t(`inbox.heading.search_results.${groupKey}`, {
             count: list.filter((i) => i.viewType === groupKey).length,
@@ -148,16 +163,21 @@ const useGroupedDialogs = ({
         : groupKey;
 
       const existingGroup = acc.find((group) => group.id === groupKey);
+
       if (existingGroup) {
         existingGroup.items.push(item);
       } else {
-        acc.push({ id: groupKey, label, items: [item] });
+        const orderIndex = getOrderIndex(createdAt, isDateKey);
+
+        acc.push({ id: groupKey, label, items: [item], orderIndex });
       }
 
       return acc;
     }, []);
 
-    const groups = Object.fromEntries(groupedItems.map(({ id, label }) => [id, { title: label }]));
+    const groups = Object.fromEntries(
+      groupedItems.map(({ id, label, orderIndex }) => [id, { title: label, orderIndex }]),
+    );
 
     const mappedGroupedDialogs = groupedItems.flatMap(({ id, items }) =>
       items.map((item) => formatDialogItem(item, id.toString())),