diff --git a/packages/app-store/googlecalendar/lib/CalendarService.ts b/packages/app-store/googlecalendar/lib/CalendarService.ts
index c4fc1a6a16..92e120f564 100644
--- a/packages/app-store/googlecalendar/lib/CalendarService.ts
+++ b/packages/app-store/googlecalendar/lib/CalendarService.ts
@@ -29,6 +29,22 @@ type FreeBusyArgs = { timeMin: string; timeMax: string; items: { id: string }[]
 
 const log = logger.getSubLogger({ prefix: ["app-store/googlecalendar/lib/CalendarService"] });
 
+/**
+ * Google system calendars that don't return proper free/busy information,
+ * making them useless for availability checking. These include:
+ * - Holiday calendars (e.g., "en.usa#holiday@group.v.calendar.google.com")
+ * - Birthdays/contacts calendar ("addressbook#contacts@group.v.calendar.google.com")
+ */
+const GOOGLE_SYSTEM_CALENDAR_SUFFIXES = [
+  "#holiday@group.v.calendar.google.com",
+  "#contacts@group.v.calendar.google.com",
+];
+
+function isGoogleSystemCalendar(calendarId: string | null | undefined): boolean {
+  if (!calendarId) return false;
+  return GOOGLE_SYSTEM_CALENDAR_SUFFIXES.some((suffix) => calendarId.endsWith(suffix));
+}
+
 /**
  * Extended interface for Google Calendar service that includes Google-specific methods.
  * This interface is used by internal Google Calendar modules (callback, tests, etc.)
@@ -710,7 +726,11 @@ class GoogleCalendarService implements Calendar {
       );
 
       if (!cals.items) return [];
-      return cals.items.map(
+
+      // Filter out Google system calendars (holidays, birthdays) as they don't return proper free/busy information
+      const filteredCalendars = cals.items.filter((cal) => !isGoogleSystemCalendar(cal.id));
+
+      return filteredCalendars.map(
         (cal) =>
           ({
             externalId: cal.id ?? "No id",
diff --git a/packages/app-store/googlecalendar/lib/__tests__/CalendarService.test.ts b/packages/app-store/googlecalendar/lib/__tests__/CalendarService.test.ts
index 149c5e264c..d95d435a01 100644
--- a/packages/app-store/googlecalendar/lib/__tests__/CalendarService.test.ts
+++ b/packages/app-store/googlecalendar/lib/__tests__/CalendarService.test.ts
@@ -803,3 +803,240 @@ describe("createEvent", () => {
     log.info("createEvent with just in time reminders test passed");
   });
 });
+
+describe("listCalendars", () => {
+  test("should filter out Google holiday calendars", async () => {
+    const calendarService = BuildCalendarService(mockCredential);
+    setFullMockOAuthManagerRequest();
+
+    calendarListMock.mockImplementation(() => {
+      return {
+        data: {
+          items: [
+            {
+              id: "user@example.com",
+              summary: "Primary Calendar",
+              primary: true,
+              accessRole: "owner",
+            },
+            {
+              id: "en.usa#holiday@group.v.calendar.google.com",
+              summary: "Holidays in United States",
+              primary: false,
+              accessRole: "reader",
+            },
+            {
+              id: "en.christian#holiday@group.v.calendar.google.com",
+              summary: "Christian Holidays",
+              primary: false,
+              accessRole: "reader",
+            },
+          ],
+        },
+      };
+    });
+
+    const calendars = await calendarService.listCalendars();
+
+    expect(calendars).toHaveLength(1);
+    expect(calendars[0].externalId).toBe("user@example.com");
+    expect(calendars[0].name).toBe("Primary Calendar");
+  });
+
+  test("should filter out Google birthdays/contacts calendar", async () => {
+    const calendarService = BuildCalendarService(mockCredential);
+    setFullMockOAuthManagerRequest();
+
+    calendarListMock.mockImplementation(() => {
+      return {
+        data: {
+          items: [
+            {
+              id: "user@example.com",
+              summary: "Primary Calendar",
+              primary: true,
+              accessRole: "owner",
+            },
+            {
+              id: "addressbook#contacts@group.v.calendar.google.com",
+              summary: "Birthdays",
+              primary: false,
+              accessRole: "reader",
+            },
+          ],
+        },
+      };
+    });
+
+    const calendars = await calendarService.listCalendars();
+
+    expect(calendars).toHaveLength(1);
+    expect(calendars[0].externalId).toBe("user@example.com");
+  });
+
+  test("should filter out all Google system calendars while keeping regular calendars", async () => {
+    const calendarService = BuildCalendarService(mockCredential);
+    setFullMockOAuthManagerRequest();
+
+    calendarListMock.mockImplementation(() => {
+      return {
+        data: {
+          items: [
+            {
+              id: "user@example.com",
+              summary: "Primary Calendar",
+              primary: true,
+              accessRole: "owner",
+            },
+            {
+              id: "work@example.com",
+              summary: "Work Calendar",
+              primary: false,
+              accessRole: "owner",
+            },
+            {
+              id: "en.usa#holiday@group.v.calendar.google.com",
+              summary: "Holidays in United States",
+              primary: false,
+              accessRole: "reader",
+            },
+            {
+              id: "addressbook#contacts@group.v.calendar.google.com",
+              summary: "Birthdays",
+              primary: false,
+              accessRole: "reader",
+            },
+            {
+              id: "shared@example.com",
+              summary: "Shared Calendar",
+              primary: false,
+              accessRole: "writer",
+            },
+          ],
+        },
+      };
+    });
+
+    const calendars = await calendarService.listCalendars();
+
+    expect(calendars).toHaveLength(3);
+    const calendarIds = calendars.map((cal) => cal.externalId);
+    expect(calendarIds).toContain("user@example.com");
+    expect(calendarIds).toContain("work@example.com");
+    expect(calendarIds).toContain("shared@example.com");
+    expect(calendarIds).not.toContain("en.usa#holiday@group.v.calendar.google.com");
+    expect(calendarIds).not.toContain("addressbook#contacts@group.v.calendar.google.com");
+  });
+
+  test("should return empty array when all calendars are system calendars", async () => {
+    const calendarService = BuildCalendarService(mockCredential);
+    setFullMockOAuthManagerRequest();
+
+    calendarListMock.mockImplementation(() => {
+      return {
+        data: {
+          items: [
+            {
+              id: "en.usa#holiday@group.v.calendar.google.com",
+              summary: "Holidays in United States",
+              primary: false,
+              accessRole: "reader",
+            },
+            {
+              id: "addressbook#contacts@group.v.calendar.google.com",
+              summary: "Birthdays",
+              primary: false,
+              accessRole: "reader",
+            },
+          ],
+        },
+      };
+    });
+
+    const calendars = await calendarService.listCalendars();
+
+    expect(calendars).toHaveLength(0);
+  });
+
+  test("should handle calendars with null or undefined ids", async () => {
+    const calendarService = BuildCalendarService(mockCredential);
+    setFullMockOAuthManagerRequest();
+
+    calendarListMock.mockImplementation(() => {
+      return {
+        data: {
+          items: [
+            {
+              id: "user@example.com",
+              summary: "Primary Calendar",
+              primary: true,
+              accessRole: "owner",
+            },
+            {
+              id: null,
+              summary: "Calendar with null id",
+              primary: false,
+              accessRole: "reader",
+            },
+            {
+              id: undefined,
+              summary: "Calendar with undefined id",
+              primary: false,
+              accessRole: "reader",
+            },
+          ],
+        },
+      };
+    });
+
+    const calendars = await calendarService.listCalendars();
+
+    expect(calendars).toHaveLength(3);
+    expect(calendars[0].externalId).toBe("user@example.com");
+    expect(calendars[1].externalId).toBe("No id");
+    expect(calendars[2].externalId).toBe("No id");
+  });
+
+  test("should correctly identify various holiday calendar formats", async () => {
+    const calendarService = BuildCalendarService(mockCredential);
+    setFullMockOAuthManagerRequest();
+
+    calendarListMock.mockImplementation(() => {
+      return {
+        data: {
+          items: [
+            {
+              id: "user@example.com",
+              summary: "Primary Calendar",
+              primary: true,
+              accessRole: "owner",
+            },
+            {
+              id: "en.uk#holiday@group.v.calendar.google.com",
+              summary: "Holidays in United Kingdom",
+              primary: false,
+              accessRole: "reader",
+            },
+            {
+              id: "de.german#holiday@group.v.calendar.google.com",
+              summary: "Holidays in Germany",
+              primary: false,
+              accessRole: "reader",
+            },
+            {
+              id: "ja.japanese#holiday@group.v.calendar.google.com",
+              summary: "Holidays in Japan",
+              primary: false,
+              accessRole: "reader",
+            },
+          ],
+        },
+      };
+    });
+
+    const calendars = await calendarService.listCalendars();
+
+    expect(calendars).toHaveLength(1);
+    expect(calendars[0].externalId).toBe("user@example.com");
+  });
+});