diff --git a/src/analytics/PosthogEvents.test.ts b/src/analytics/PosthogEvents.test.ts
new file mode 100644
index 00000000..35b86f5d
--- /dev/null
+++ b/src/analytics/PosthogEvents.test.ts
@@ -0,0 +1,162 @@
+/*
+Copyright 2025 New Vector Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import {
+  expect,
+  describe,
+  it,
+  vi,
+  beforeEach,
+  beforeAll,
+  afterAll,
+} from "vitest";
+import { logger } from "matrix-js-sdk/lib/logger";
+import { type MatrixRTCSession } from "matrix-js-sdk/lib/matrixrtc";
+
+import { PosthogAnalytics } from "./PosthogAnalytics";
+import { CallEndedTracker } from "./PosthogEvents";
+import { mockConfig } from "../utils/test";
+
+const defaultCounters = {
+  roomEventEncryptionKeysSent: 10,
+  roomEventEncryptionKeysReceived: 5,
+};
+
+const defaultTotals = {
+  roomEventEncryptionKeysReceivedTotalAge: 500,
+};
+
+function createMockRtcSession(overrides?: {
+  counters?: Partial<typeof defaultCounters>;
+  totals?: Partial<typeof defaultTotals>;
+}): MatrixRTCSession {
+  return {
+    statistics: {
+      counters: { ...defaultCounters, ...overrides?.counters },
+      totals: { ...defaultTotals, ...overrides?.totals },
+    },
+  } as unknown as MatrixRTCSession;
+}
+
+describe("CallEnded", () => {
+  beforeAll(() => {
+    mockConfig();
+  });
+
+  beforeEach(() => {
+    vi.restoreAllMocks();
+    vi.spyOn(PosthogAnalytics.instance, "trackEvent").mockImplementation(
+      () => {},
+    );
+  });
+
+  afterAll(() => {
+    PosthogAnalytics.resetInstance();
+  });
+
+  it("warns if startTime is missing when track is called", () => {
+    const warnSpy = vi.spyOn(logger, "warn");
+    const tracker = new CallEndedTracker();
+    const mockSession = createMockRtcSession();
+
+    tracker.track("test-call-id", 2, false, mockSession);
+
+    expect(warnSpy).toHaveBeenCalledWith(
+      "[PosthogEvents] Failed to send posthog callEnded event due to missing startTime",
+    );
+    expect(PosthogAnalytics.instance.trackEvent).not.toHaveBeenCalled();
+  });
+
+  it("tracks event with correct properties when startTime is set", () => {
+    const tracker = new CallEndedTracker();
+    const mockSession = createMockRtcSession();
+
+    tracker.cacheStartCall(new Date(Date.now() - 60000));
+    tracker.cacheParticipantCountChanged(5);
+    tracker.track("test-call-id", 3, true, mockSession);
+
+    expect(PosthogAnalytics.instance.trackEvent).toHaveBeenCalledWith(
+      {
+        eventName: "CallEnded",
+        callId: "test-call-id",
+        callParticipantsMax: 5,
+        callParticipantsOnLeave: 3,
+        callDuration: expect.closeTo(60, 1),
+        roomEventEncryptionKeysSent: 10,
+        roomEventEncryptionKeysReceived: 5,
+        roomEventEncryptionKeysReceivedAverageAge: 100,
+      },
+      { send_instantly: true },
+    );
+  });
+
+  it("tracks maxParticipantsCount correctly across multiple changes", () => {
+    const tracker = new CallEndedTracker();
+    const mockSession = createMockRtcSession();
+
+    tracker.cacheStartCall(new Date());
+    tracker.cacheParticipantCountChanged(3);
+    tracker.cacheParticipantCountChanged(7);
+    tracker.cacheParticipantCountChanged(2);
+    tracker.track("test-call-id", 1, false, mockSession);
+
+    expect(PosthogAnalytics.instance.trackEvent).toHaveBeenCalledWith(
+      expect.objectContaining({
+        callParticipantsMax: 7,
+      }),
+      expect.anything(),
+    );
+  });
+
+  it("computes roomEventEncryptionKeysReceivedAverageAge as 0 when no keys received", () => {
+    const tracker = new CallEndedTracker();
+    const mockSession = createMockRtcSession({
+      counters: { roomEventEncryptionKeysReceived: 0 },
+    });
+
+    tracker.cacheStartCall(new Date());
+    tracker.track("test-call-id", 1, false, mockSession);
+
+    expect(PosthogAnalytics.instance.trackEvent).toHaveBeenCalledWith(
+      expect.objectContaining({
+        roomEventEncryptionKeysReceivedAverageAge: 0,
+      }),
+      expect.anything(),
+    );
+  });
+
+  it("computes roomEventEncryptionKeysReceivedAverageAge correctly when keys are received", () => {
+    const tracker = new CallEndedTracker();
+    const mockSession = createMockRtcSession({
+      counters: { roomEventEncryptionKeysReceived: 4 },
+      totals: { roomEventEncryptionKeysReceivedTotalAge: 200 },
+    });
+
+    tracker.cacheStartCall(new Date());
+    tracker.track("test-call-id", 1, false, mockSession);
+
+    expect(PosthogAnalytics.instance.trackEvent).toHaveBeenCalledWith(
+      expect.objectContaining({
+        roomEventEncryptionKeysReceivedAverageAge: 50,
+      }),
+      expect.anything(),
+    );
+  });
+
+  it("passes send_instantly option correctly", () => {
+    const tracker = new CallEndedTracker();
+    const mockSession = createMockRtcSession();
+
+    tracker.cacheStartCall(new Date());
+    tracker.track("test-call-id", 1, false, mockSession);
+
+    expect(PosthogAnalytics.instance.trackEvent).toHaveBeenCalledWith(
+      expect.anything(),
+      { send_instantly: false },
+    );
+  });
+});
diff --git a/src/analytics/PosthogEvents.ts b/src/analytics/PosthogEvents.ts
index f0f059f5..5553829a 100644
--- a/src/analytics/PosthogEvents.ts
+++ b/src/analytics/PosthogEvents.ts
@@ -27,8 +27,8 @@ interface CallEnded extends IPosthogEvent {
 }
 
 export class CallEndedTracker {
-  private cache: { startTime: Date; maxParticipantsCount: number } = {
-    startTime: new Date(0),
+  private cache: { startTime?: Date; maxParticipantsCount: number } = {
+    startTime: undefined,
     maxParticipantsCount: 0,
   };
 
@@ -49,26 +49,32 @@ export class CallEndedTracker {
     sendInstantly: boolean,
     rtcSession: MatrixRTCSession,
   ): void {
-    PosthogAnalytics.instance.trackEvent<CallEnded>(
-      {
-        eventName: "CallEnded",
-        callId: callId,
-        callParticipantsMax: this.cache.maxParticipantsCount,
-        callParticipantsOnLeave: callParticipantsNow,
-        callDuration: (Date.now() - this.cache.startTime.getTime()) / 1000,
-        roomEventEncryptionKeysSent:
-          rtcSession.statistics.counters.roomEventEncryptionKeysSent,
-        roomEventEncryptionKeysReceived:
-          rtcSession.statistics.counters.roomEventEncryptionKeysReceived,
-        roomEventEncryptionKeysReceivedAverageAge:
-          rtcSession.statistics.counters.roomEventEncryptionKeysReceived > 0
-            ? rtcSession.statistics.totals
-                .roomEventEncryptionKeysReceivedTotalAge /
-              rtcSession.statistics.counters.roomEventEncryptionKeysReceived
-            : 0,
-      },
-      { send_instantly: sendInstantly },
-    );
+    if (this.cache.startTime) {
+      PosthogAnalytics.instance.trackEvent<CallEnded>(
+        {
+          eventName: "CallEnded",
+          callId: callId,
+          callParticipantsMax: this.cache.maxParticipantsCount,
+          callParticipantsOnLeave: callParticipantsNow,
+          callDuration: (Date.now() - this.cache.startTime.getTime()) / 1000,
+          roomEventEncryptionKeysSent:
+            rtcSession.statistics.counters.roomEventEncryptionKeysSent,
+          roomEventEncryptionKeysReceived:
+            rtcSession.statistics.counters.roomEventEncryptionKeysReceived,
+          roomEventEncryptionKeysReceivedAverageAge:
+            rtcSession.statistics.counters.roomEventEncryptionKeysReceived > 0
+              ? rtcSession.statistics.totals
+                  .roomEventEncryptionKeysReceivedTotalAge /
+                rtcSession.statistics.counters.roomEventEncryptionKeysReceived
+              : 0,
+        },
+        { send_instantly: sendInstantly },
+      );
+    } else {
+      logger.warn(
+        "[PosthogEvents] Failed to send posthog callEnded event due to missing startTime",
+      );
+    }
   }
 }