diff --git a/homeassistant/components/timer/__init__.py b/homeassistant/components/timer/__init__.py
index 35258555537..63ab766567d 100644
--- a/homeassistant/components/timer/__init__.py
+++ b/homeassistant/components/timer/__init__.py
@@ -9,6 +9,7 @@ import voluptuous as vol
 
 from homeassistant.const import (
     ATTR_EDITABLE,
+    ATTR_ENTITY_ID,
     CONF_ICON,
     CONF_ID,
     CONF_NAME,
@@ -31,10 +32,16 @@ DOMAIN = "timer"
 ENTITY_ID_FORMAT = DOMAIN + ".{}"
 
 DEFAULT_DURATION = 0
+DEFAULT_RESTORE = False
+
 ATTR_DURATION = "duration"
 ATTR_REMAINING = "remaining"
 ATTR_FINISHES_AT = "finishes_at"
+ATTR_RESTORE = "restore"
+ATTR_FINISHED_AT = "finished_at"
+
 CONF_DURATION = "duration"
+CONF_RESTORE = "restore"
 
 STATUS_IDLE = "idle"
 STATUS_ACTIVE = "active"
@@ -58,11 +65,13 @@ CREATE_FIELDS = {
     vol.Required(CONF_NAME): cv.string,
     vol.Optional(CONF_ICON): cv.icon,
     vol.Optional(CONF_DURATION, default=DEFAULT_DURATION): cv.time_period,
+    vol.Optional(CONF_RESTORE, default=DEFAULT_RESTORE): cv.boolean,
 }
 UPDATE_FIELDS = {
     vol.Optional(CONF_NAME): cv.string,
     vol.Optional(CONF_ICON): cv.icon,
     vol.Optional(CONF_DURATION): cv.time_period,
+    vol.Optional(CONF_RESTORE): cv.boolean,
 }
 
 
@@ -90,6 +99,7 @@ CONFIG_SCHEMA = vol.Schema(
                     vol.Optional(CONF_DURATION, default=DEFAULT_DURATION): vol.All(
                         cv.time_period, _format_timedelta
                     ),
+                    vol.Optional(CONF_RESTORE, default=DEFAULT_RESTORE): cv.boolean,
                 },
             )
         )
@@ -197,6 +207,7 @@ class Timer(RestoreEntity):
         self._remaining: timedelta | None = None
         self._end: datetime | None = None
         self._listener: Callable[[], None] | None = None
+        self._restore: bool = self._config[CONF_RESTORE]
 
         self._attr_should_poll = False
         self._attr_force_update = True
@@ -235,6 +246,8 @@ class Timer(RestoreEntity):
             attrs[ATTR_FINISHES_AT] = self._end.isoformat()
         if self._remaining is not None:
             attrs[ATTR_REMAINING] = _format_timedelta(self._remaining)
+        if self._restore:
+            attrs[ATTR_RESTORE] = self._restore
 
         return attrs
 
@@ -245,15 +258,41 @@ class Timer(RestoreEntity):
 
     async def async_added_to_hass(self):
         """Call when entity is about to be added to Home Assistant."""
-        # If not None, we got an initial value.
-        if self._state is not None:
+        # If we don't need to restore a previous state or no previous state exists,
+        # start at idle
+        if not self._restore or (state := await self.async_get_last_state()) is None:
+            self._state = STATUS_IDLE
             return
 
-        state = await self.async_get_last_state()
-        self._state = state and state.state == state
+        # Begin restoring state
+        self._state = state.state
+        self._duration = cv.time_period(state.attributes[ATTR_DURATION])
+
+        # Nothing more to do if the timer is idle
+        if self._state == STATUS_IDLE:
+            return
+
+        # If the timer was paused, we restore the remaining time
+        if self._state == STATUS_PAUSED:
+            self._remaining = cv.time_period(state.attributes[ATTR_REMAINING])
+            return
+        # If we get here, the timer must have been active so we need to decide what
+        # to do based on end time and the current time
+        end = cv.datetime(state.attributes[ATTR_FINISHES_AT])
+        # If there is time remaining in the timer, restore the remaining time then
+        # start the timer
+        if (remaining := end - dt_util.utcnow().replace(microsecond=0)) > timedelta(0):
+            self._remaining = remaining
+            self._state = STATUS_PAUSED
+            self.async_start()
+        # If the timer ended before now, finish the timer. The event will indicate
+        # when the timer was expected to fire.
+        else:
+            self._end = end
+            self.async_finish()
 
     @callback
-    def async_start(self, duration: timedelta):
+    def async_start(self, duration: timedelta | None = None):
         """Start a timer."""
         if self._listener:
             self._listener()
@@ -274,7 +313,7 @@ class Timer(RestoreEntity):
 
         self._end = start + self._remaining
 
-        self.hass.bus.async_fire(event, {"entity_id": self.entity_id})
+        self.hass.bus.async_fire(event, {ATTR_ENTITY_ID: self.entity_id})
 
         self._listener = async_track_point_in_utc_time(
             self.hass, self._async_finished, self._end
@@ -292,7 +331,7 @@ class Timer(RestoreEntity):
         self._remaining = self._end - dt_util.utcnow().replace(microsecond=0)
         self._state = STATUS_PAUSED
         self._end = None
-        self.hass.bus.async_fire(EVENT_TIMER_PAUSED, {"entity_id": self.entity_id})
+        self.hass.bus.async_fire(EVENT_TIMER_PAUSED, {ATTR_ENTITY_ID: self.entity_id})
         self.async_write_ha_state()
 
     @callback
@@ -304,7 +343,9 @@ class Timer(RestoreEntity):
         self._state = STATUS_IDLE
         self._end = None
         self._remaining = None
-        self.hass.bus.async_fire(EVENT_TIMER_CANCELLED, {"entity_id": self.entity_id})
+        self.hass.bus.async_fire(
+            EVENT_TIMER_CANCELLED, {ATTR_ENTITY_ID: self.entity_id}
+        )
         self.async_write_ha_state()
 
     @callback
@@ -316,10 +357,14 @@ class Timer(RestoreEntity):
         if self._listener:
             self._listener()
             self._listener = None
+        end = self._end
         self._state = STATUS_IDLE
         self._end = None
         self._remaining = None
-        self.hass.bus.async_fire(EVENT_TIMER_FINISHED, {"entity_id": self.entity_id})
+        self.hass.bus.async_fire(
+            EVENT_TIMER_FINISHED,
+            {ATTR_ENTITY_ID: self.entity_id, ATTR_FINISHED_AT: end.isoformat()},
+        )
         self.async_write_ha_state()
 
     @callback
@@ -330,13 +375,18 @@ class Timer(RestoreEntity):
 
         self._listener = None
         self._state = STATUS_IDLE
+        end = self._end
         self._end = None
         self._remaining = None
-        self.hass.bus.async_fire(EVENT_TIMER_FINISHED, {"entity_id": self.entity_id})
+        self.hass.bus.async_fire(
+            EVENT_TIMER_FINISHED,
+            {ATTR_ENTITY_ID: self.entity_id, ATTR_FINISHED_AT: end.isoformat()},
+        )
         self.async_write_ha_state()
 
     async def async_update_config(self, config: dict) -> None:
         """Handle when the config is updated."""
         self._config = config
         self._duration = cv.time_period_str(config[CONF_DURATION])
+        self._restore = config[CONF_RESTORE]
         self.async_write_ha_state()
diff --git a/tests/components/timer/test_init.py b/tests/components/timer/test_init.py
index 5c276bc0cfc..8f605d2de9f 100644
--- a/tests/components/timer/test_init.py
+++ b/tests/components/timer/test_init.py
@@ -8,10 +8,13 @@ import pytest
 
 from homeassistant.components.timer import (
     ATTR_DURATION,
+    ATTR_FINISHES_AT,
     ATTR_REMAINING,
+    ATTR_RESTORE,
     CONF_DURATION,
     CONF_ICON,
     CONF_NAME,
+    CONF_RESTORE,
     DEFAULT_DURATION,
     DOMAIN,
     EVENT_TIMER_CANCELLED,
@@ -26,6 +29,7 @@ from homeassistant.components.timer import (
     STATUS_ACTIVE,
     STATUS_IDLE,
     STATUS_PAUSED,
+    Timer,
     _format_timedelta,
 )
 from homeassistant.const import (
@@ -35,16 +39,22 @@ from homeassistant.const import (
     ATTR_ID,
     ATTR_NAME,
     CONF_ENTITY_ID,
+    CONF_ID,
     EVENT_STATE_CHANGED,
     SERVICE_RELOAD,
 )
-from homeassistant.core import Context, CoreState
+from homeassistant.core import Context, CoreState, State
 from homeassistant.exceptions import Unauthorized
 from homeassistant.helpers import config_validation as cv, entity_registry as er
+from homeassistant.helpers.restore_state import (
+    DATA_RESTORE_STATE_TASK,
+    RestoreStateData,
+    StoredState,
+)
 from homeassistant.setup import async_setup_component
 from homeassistant.util.dt import utcnow
 
-from tests.common import async_fire_time_changed
+from tests.common import async_capture_events, async_fire_time_changed
 
 _LOGGER = logging.getLogger(__name__)
 
@@ -64,6 +74,7 @@ def storage_setup(hass, hass_storage):
                             ATTR_ID: "from_storage",
                             ATTR_NAME: "timer from storage",
                             ATTR_DURATION: "0:00:00",
+                            ATTR_RESTORE: False,
                         }
                     ]
                 },
@@ -580,6 +591,7 @@ async def test_update(hass, hass_ws_client, storage_setup):
             "type": f"{DOMAIN}/update",
             f"{DOMAIN}_id": f"{timer_id}",
             CONF_DURATION: 33,
+            CONF_RESTORE: True,
         }
     )
     resp = await client.receive_json()
@@ -587,6 +599,7 @@ async def test_update(hass, hass_ws_client, storage_setup):
 
     state = hass.states.get(timer_entity_id)
     assert state.attributes[ATTR_DURATION] == _format_timedelta(cv.time_period(33))
+    assert state.attributes[ATTR_RESTORE]
 
 
 async def test_ws_create(hass, hass_ws_client, storage_setup):
@@ -637,3 +650,183 @@ async def test_setup_no_config(hass, hass_admin_user):
         await hass.async_block_till_done()
 
     assert count_start == len(hass.states.async_entity_ids())
+
+
+async def test_restore_idle(hass):
+    """Test entity restore logic when timer is idle."""
+    utc_now = utcnow()
+    stored_state = StoredState(
+        State(
+            "timer.test",
+            STATUS_IDLE,
+            {ATTR_DURATION: "0:00:30"},
+        ),
+        None,
+        utc_now,
+    )
+
+    data = await RestoreStateData.async_get_instance(hass)
+    await hass.async_block_till_done()
+    await data.store.async_save([stored_state.as_dict()])
+
+    # Emulate a fresh load
+    hass.data.pop(DATA_RESTORE_STATE_TASK)
+
+    entity = Timer(
+        {
+            CONF_ID: "test",
+            CONF_NAME: "test",
+            CONF_DURATION: "0:01:00",
+            CONF_RESTORE: True,
+        }
+    )
+    entity.hass = hass
+    entity.entity_id = "timer.test"
+
+    await entity.async_added_to_hass()
+    await hass.async_block_till_done()
+    assert entity.state == STATUS_IDLE
+    assert entity.extra_state_attributes[ATTR_DURATION] == "0:00:30"
+    assert ATTR_REMAINING not in entity.extra_state_attributes
+    assert ATTR_FINISHES_AT not in entity.extra_state_attributes
+    assert entity.extra_state_attributes[ATTR_RESTORE]
+
+
+async def test_restore_paused(hass):
+    """Test entity restore logic when timer is paused."""
+    utc_now = utcnow()
+    stored_state = StoredState(
+        State(
+            "timer.test",
+            STATUS_PAUSED,
+            {ATTR_DURATION: "0:00:30", ATTR_REMAINING: "0:00:15"},
+        ),
+        None,
+        utc_now,
+    )
+
+    data = await RestoreStateData.async_get_instance(hass)
+    await hass.async_block_till_done()
+    await data.store.async_save([stored_state.as_dict()])
+
+    # Emulate a fresh load
+    hass.data.pop(DATA_RESTORE_STATE_TASK)
+
+    entity = Timer(
+        {
+            CONF_ID: "test",
+            CONF_NAME: "test",
+            CONF_DURATION: "0:01:00",
+            CONF_RESTORE: True,
+        }
+    )
+    entity.hass = hass
+    entity.entity_id = "timer.test"
+
+    await entity.async_added_to_hass()
+    await hass.async_block_till_done()
+    assert entity.state == STATUS_PAUSED
+    assert entity.extra_state_attributes[ATTR_DURATION] == "0:00:30"
+    assert entity.extra_state_attributes[ATTR_REMAINING] == "0:00:15"
+    assert ATTR_FINISHES_AT not in entity.extra_state_attributes
+    assert entity.extra_state_attributes[ATTR_RESTORE]
+
+
+async def test_restore_active_resume(hass):
+    """Test entity restore logic when timer is active and end time is after startup."""
+    events = async_capture_events(hass, EVENT_TIMER_RESTARTED)
+    assert not events
+    utc_now = utcnow()
+    finish = utc_now + timedelta(seconds=30)
+    simulated_utc_now = utc_now + timedelta(seconds=15)
+    stored_state = StoredState(
+        State(
+            "timer.test",
+            STATUS_ACTIVE,
+            {ATTR_DURATION: "0:00:30", ATTR_FINISHES_AT: finish.isoformat()},
+        ),
+        None,
+        utc_now,
+    )
+
+    data = await RestoreStateData.async_get_instance(hass)
+    await hass.async_block_till_done()
+    await data.store.async_save([stored_state.as_dict()])
+
+    # Emulate a fresh load
+    hass.data.pop(DATA_RESTORE_STATE_TASK)
+
+    entity = Timer(
+        {
+            CONF_ID: "test",
+            CONF_NAME: "test",
+            CONF_DURATION: "0:01:00",
+            CONF_RESTORE: True,
+        }
+    )
+    entity.hass = hass
+    entity.entity_id = "timer.test"
+
+    # In patch make sure we ignore microseconds
+    with patch(
+        "homeassistant.components.timer.dt_util.utcnow",
+        return_value=simulated_utc_now.replace(microsecond=999),
+    ):
+        await entity.async_added_to_hass()
+        await hass.async_block_till_done()
+
+    assert entity.state == STATUS_ACTIVE
+    assert entity.extra_state_attributes[ATTR_DURATION] == "0:00:30"
+    assert entity.extra_state_attributes[ATTR_REMAINING] == "0:00:15"
+    assert entity.extra_state_attributes[ATTR_FINISHES_AT] == finish.isoformat()
+    assert entity.extra_state_attributes[ATTR_RESTORE]
+    assert len(events) == 1
+
+
+async def test_restore_active_finished_outside_grace(hass):
+    """Test entity restore logic: timer is active, ended while Home Assistant was stopped."""
+    events = async_capture_events(hass, EVENT_TIMER_FINISHED)
+    assert not events
+    utc_now = utcnow()
+    finish = utc_now + timedelta(seconds=30)
+    simulated_utc_now = utc_now + timedelta(seconds=46)
+    stored_state = StoredState(
+        State(
+            "timer.test",
+            STATUS_ACTIVE,
+            {ATTR_DURATION: "0:00:30", ATTR_FINISHES_AT: finish.isoformat()},
+        ),
+        None,
+        utc_now,
+    )
+
+    data = await RestoreStateData.async_get_instance(hass)
+    await hass.async_block_till_done()
+    await data.store.async_save([stored_state.as_dict()])
+
+    # Emulate a fresh load
+    hass.data.pop(DATA_RESTORE_STATE_TASK)
+
+    entity = Timer(
+        {
+            CONF_ID: "test",
+            CONF_NAME: "test",
+            CONF_DURATION: "0:01:00",
+            CONF_RESTORE: True,
+        }
+    )
+    entity.hass = hass
+    entity.entity_id = "timer.test"
+
+    with patch(
+        "homeassistant.components.timer.dt_util.utcnow", return_value=simulated_utc_now
+    ):
+        await entity.async_added_to_hass()
+        await hass.async_block_till_done()
+
+    assert entity.state == STATUS_IDLE
+    assert entity.extra_state_attributes[ATTR_DURATION] == "0:00:30"
+    assert ATTR_REMAINING not in entity.extra_state_attributes
+    assert ATTR_FINISHES_AT not in entity.extra_state_attributes
+    assert entity.extra_state_attributes[ATTR_RESTORE]
+    assert len(events) == 1