diff --git a/homeassistant/components/google/calendar.py b/homeassistant/components/google/calendar.py
index b52f120e65a..73071e8a13d 100644
--- a/homeassistant/components/google/calendar.py
+++ b/homeassistant/components/google/calendar.py
@@ -120,13 +120,22 @@ class GoogleCalendarEntity(CalendarEntity):
         self._event: CalendarEvent | None = None
         self._name: str = data[CONF_NAME]
         self._offset = data.get(CONF_OFFSET, DEFAULT_CONF_OFFSET)
-        self._offset_reached = False
+        self._offset_value: timedelta | None = None
         self.entity_id = entity_id
 
     @property
     def extra_state_attributes(self) -> dict[str, bool]:
         """Return the device state attributes."""
-        return {"offset_reached": self._offset_reached}
+        return {"offset_reached": self.offset_reached}
+
+    @property
+    def offset_reached(self) -> bool:
+        """Return whether or not the event offset was reached."""
+        if self._event and self._offset_value:
+            return is_offset_reached(
+                self._event.start_datetime_local, self._offset_value
+            )
+        return False
 
     @property
     def event(self) -> CalendarEvent | None:
@@ -187,9 +196,7 @@ class GoogleCalendarEntity(CalendarEntity):
             (summary, offset) = extract_offset(event.get("summary", ""), self._offset)
             event["summary"] = summary
             self._event = _get_calendar_event(event)
-            self._offset_reached = is_offset_reached(
-                self._event.start_datetime_local, offset
-            )
+            self._offset_value = offset
         else:
             self._event = None
 
diff --git a/tests/components/google/test_calendar.py b/tests/components/google/test_calendar.py
index a5aca8a27d4..dda4cddc962 100644
--- a/tests/components/google/test_calendar.py
+++ b/tests/components/google/test_calendar.py
@@ -505,3 +505,77 @@ async def test_scan_calendar_error(
         assert await component_setup()
 
     assert not hass.states.get(TEST_ENTITY)
+
+
+async def test_future_event_update_behavior(
+    hass, mock_events_list_items, component_setup
+):
+    """Test an future event that becomes active."""
+    now = dt_util.now()
+    now_utc = dt_util.utcnow()
+    one_hour_from_now = now + datetime.timedelta(minutes=60)
+    end_event = one_hour_from_now + datetime.timedelta(minutes=90)
+    event = {
+        **TEST_EVENT,
+        "start": {"dateTime": one_hour_from_now.isoformat()},
+        "end": {"dateTime": end_event.isoformat()},
+    }
+    mock_events_list_items([event])
+    assert await component_setup()
+
+    # Event has not started yet
+    state = hass.states.get(TEST_ENTITY)
+    assert state.name == TEST_ENTITY_NAME
+    assert state.state == STATE_OFF
+
+    # Advance time until event has started
+    now += datetime.timedelta(minutes=60)
+    now_utc += datetime.timedelta(minutes=30)
+    with patch("homeassistant.util.dt.utcnow", return_value=now_utc), patch(
+        "homeassistant.util.dt.now", return_value=now
+    ):
+        async_fire_time_changed(hass, now)
+        await hass.async_block_till_done()
+
+    # Event has started
+    state = hass.states.get(TEST_ENTITY)
+    assert state.state == STATE_ON
+
+
+async def test_future_event_offset_update_behavior(
+    hass, mock_events_list_items, component_setup
+):
+    """Test an future event that becomes active."""
+    now = dt_util.now()
+    now_utc = dt_util.utcnow()
+    one_hour_from_now = now + datetime.timedelta(minutes=60)
+    end_event = one_hour_from_now + datetime.timedelta(minutes=90)
+    event_summary = "Test Event in Progress"
+    event = {
+        **TEST_EVENT,
+        "start": {"dateTime": one_hour_from_now.isoformat()},
+        "end": {"dateTime": end_event.isoformat()},
+        "summary": f"{event_summary} !!-15",
+    }
+    mock_events_list_items([event])
+    assert await component_setup()
+
+    # Event has not started yet
+    state = hass.states.get(TEST_ENTITY)
+    assert state.name == TEST_ENTITY_NAME
+    assert state.state == STATE_OFF
+    assert not state.attributes["offset_reached"]
+
+    # Advance time until event has started
+    now += datetime.timedelta(minutes=45)
+    now_utc += datetime.timedelta(minutes=45)
+    with patch("homeassistant.util.dt.utcnow", return_value=now_utc), patch(
+        "homeassistant.util.dt.now", return_value=now
+    ):
+        async_fire_time_changed(hass, now)
+        await hass.async_block_till_done()
+
+    # Event has not started, but the offset was reached
+    state = hass.states.get(TEST_ENTITY)
+    assert state.state == STATE_OFF
+    assert state.attributes["offset_reached"]