diff --git a/homeassistant/components/group/cover.py b/homeassistant/components/group/cover.py
index 64baba6d1e86..e258c662bc7c 100644
--- a/homeassistant/components/group/cover.py
+++ b/homeassistant/components/group/cover.py
@@ -282,6 +282,7 @@ class CoverGroup(GroupEntity, CoverEntity):
         self._attr_is_closed = True
         self._attr_is_closing = False
         self._attr_is_opening = False
+        self._update_assumed_state_from_members()
         for entity_id in self._entity_ids:
             if not (state := self.hass.states.get(entity_id)):
                 continue
diff --git a/homeassistant/components/group/entity.py b/homeassistant/components/group/entity.py
index 40db70a2eb35..f9d9a62a0ac7 100644
--- a/homeassistant/components/group/entity.py
+++ b/homeassistant/components/group/entity.py
@@ -115,6 +115,17 @@ class GroupEntity(Entity):
     def async_update_group_state(self) -> None:
         """Abstract method to update the entity."""
 
+    @callback
+    def _update_assumed_state_from_members(self) -> None:
+        """Update assumed_state based on member entities."""
+        self._attr_assumed_state = False
+        for entity_id in self._entity_ids:
+            if (state := self.hass.states.get(entity_id)) is None:
+                continue
+            if state.attributes.get(ATTR_ASSUMED_STATE):
+                self._attr_assumed_state = True
+                return
+
     @callback
     def async_update_supported_features(
         self,
diff --git a/homeassistant/components/group/fan.py b/homeassistant/components/group/fan.py
index 78745cb74c60..621c00bb1567 100644
--- a/homeassistant/components/group/fan.py
+++ b/homeassistant/components/group/fan.py
@@ -252,6 +252,7 @@ class FanGroup(GroupEntity, FanEntity):
     @callback
     def async_update_group_state(self) -> None:
         """Update state and attributes."""
+        self._update_assumed_state_from_members()
 
         states = [
             state
diff --git a/homeassistant/components/group/light.py b/homeassistant/components/group/light.py
index 259832d6152d..564a9f12ed99 100644
--- a/homeassistant/components/group/light.py
+++ b/homeassistant/components/group/light.py
@@ -205,6 +205,8 @@ class LightGroup(GroupEntity, LightEntity):
     @callback
     def async_update_group_state(self) -> None:
         """Query all members and determine the light group state."""
+        self._update_assumed_state_from_members()
+
         states = [
             state
             for entity_id in self._entity_ids
diff --git a/homeassistant/components/group/switch.py b/homeassistant/components/group/switch.py
index 29e625ca8e36..0a13e2cf2051 100644
--- a/homeassistant/components/group/switch.py
+++ b/homeassistant/components/group/switch.py
@@ -156,6 +156,8 @@ class SwitchGroup(GroupEntity, SwitchEntity):
     @callback
     def async_update_group_state(self) -> None:
         """Query all members and determine the switch group state."""
+        self._update_assumed_state_from_members()
+
         states = [
             state.state
             for entity_id in self._entity_ids
diff --git a/tests/components/group/test_cover.py b/tests/components/group/test_cover.py
index ab92b18cc91f..a8fe0f8d96e0 100644
--- a/tests/components/group/test_cover.py
+++ b/tests/components/group/test_cover.py
@@ -421,13 +421,6 @@ async def test_attributes(
     assert ATTR_CURRENT_POSITION not in state.attributes
     assert ATTR_CURRENT_TILT_POSITION not in state.attributes
 
-    # Group member has set assumed_state
-    hass.states.async_set(DEMO_TILT, CoverState.CLOSED, {ATTR_ASSUMED_STATE: True})
-    await hass.async_block_till_done()
-
-    state = hass.states.get(COVER_GROUP)
-    assert ATTR_ASSUMED_STATE not in state.attributes
-
     # Test entity registry integration
     entry = entity_registry.async_get(COVER_GROUP)
     assert entry
@@ -859,6 +852,61 @@ async def test_is_opening_closing(hass: HomeAssistant) -> None:
     assert hass.states.get(COVER_GROUP).state == CoverState.OPENING
 
 
+@pytest.mark.parametrize("config_count", [(CONFIG_ATTRIBUTES, 1)])
+@pytest.mark.usefixtures("setup_comp")
+async def test_assumed_state(hass: HomeAssistant) -> None:
+    """Test assumed_state attribute behavior."""
+    # No members with assumed_state -> group doesn't have assumed_state in attributes
+    hass.states.async_set(DEMO_COVER, CoverState.OPEN, {})
+    hass.states.async_set(DEMO_COVER_POS, CoverState.OPEN, {})
+    hass.states.async_set(DEMO_COVER_TILT, CoverState.CLOSED, {})
+    hass.states.async_set(DEMO_TILT, CoverState.CLOSED, {})
+    await hass.async_block_till_done()
+
+    state = hass.states.get(COVER_GROUP)
+    assert ATTR_ASSUMED_STATE not in state.attributes
+
+    # One member with assumed_state=True -> group has assumed_state=True
+    hass.states.async_set(DEMO_COVER, CoverState.OPEN, {ATTR_ASSUMED_STATE: True})
+    await hass.async_block_till_done()
+
+    state = hass.states.get(COVER_GROUP)
+    assert state.attributes.get(ATTR_ASSUMED_STATE) is True
+
+    # Multiple members with assumed_state=True -> group has assumed_state=True
+    hass.states.async_set(
+        DEMO_COVER_TILT, CoverState.CLOSED, {ATTR_ASSUMED_STATE: True}
+    )
+    hass.states.async_set(DEMO_TILT, CoverState.CLOSED, {ATTR_ASSUMED_STATE: True})
+    await hass.async_block_till_done()
+
+    state = hass.states.get(COVER_GROUP)
+    assert state.attributes.get(ATTR_ASSUMED_STATE) is True
+
+    # Unavailable member with assumed_state=True -> group has assumed_state=True
+    hass.states.async_set(DEMO_COVER, CoverState.OPEN, {})
+    hass.states.async_set(DEMO_COVER_TILT, CoverState.CLOSED, {})
+    hass.states.async_set(DEMO_TILT, STATE_UNAVAILABLE, {ATTR_ASSUMED_STATE: True})
+    await hass.async_block_till_done()
+
+    state = hass.states.get(COVER_GROUP)
+    assert state.attributes.get(ATTR_ASSUMED_STATE) is True
+
+    # Unknown member with assumed_state=True -> group has assumed_state=True
+    hass.states.async_set(DEMO_TILT, STATE_UNKNOWN, {ATTR_ASSUMED_STATE: True})
+    await hass.async_block_till_done()
+
+    state = hass.states.get(COVER_GROUP)
+    assert state.attributes.get(ATTR_ASSUMED_STATE) is True
+
+    # All members without assumed_state -> group doesn't have assumed_state in attributes
+    hass.states.async_set(DEMO_TILT, CoverState.CLOSED, {})
+    await hass.async_block_till_done()
+
+    state = hass.states.get(COVER_GROUP)
+    assert ATTR_ASSUMED_STATE not in state.attributes
+
+
 async def test_nested_group(hass: HomeAssistant) -> None:
     """Test nested cover group."""
     await async_setup_component(
diff --git a/tests/components/group/test_fan.py b/tests/components/group/test_fan.py
index 93509b5a651e..96c2cb33f6a1 100644
--- a/tests/components/group/test_fan.py
+++ b/tests/components/group/test_fan.py
@@ -587,3 +587,47 @@ async def test_nested_group(hass: HomeAssistant) -> None:
     assert hass.states.get(PERCENTAGE_FULL_FAN_ENTITY_ID).state == STATE_ON
     assert hass.states.get("fan.bedroom_group").state == STATE_ON
     assert hass.states.get("fan.nested_group").state == STATE_ON
+
+
+async def test_assumed_state(hass: HomeAssistant) -> None:
+    """Test assumed_state attribute behavior."""
+    await async_setup_component(
+        hass,
+        FAN_DOMAIN,
+        {
+            FAN_DOMAIN: [
+                {"platform": "demo"},
+                {
+                    "platform": "group",
+                    CONF_ENTITIES: [LIVING_ROOM_FAN_ENTITY_ID, CEILING_FAN_ENTITY_ID],
+                },
+            ]
+        },
+    )
+    await hass.async_block_till_done()
+    await hass.async_start()
+    await hass.async_block_till_done()
+
+    # No members with assumed_state -> group doesn't have assumed_state in attributes
+    hass.states.async_set(LIVING_ROOM_FAN_ENTITY_ID, STATE_ON, {})
+    hass.states.async_set(CEILING_FAN_ENTITY_ID, STATE_OFF, {})
+    await hass.async_block_till_done()
+
+    state = hass.states.get(FAN_GROUP)
+    assert ATTR_ASSUMED_STATE not in state.attributes
+
+    # One member with assumed_state=True -> group has assumed_state=True
+    hass.states.async_set(
+        LIVING_ROOM_FAN_ENTITY_ID, STATE_ON, {ATTR_ASSUMED_STATE: True}
+    )
+    await hass.async_block_till_done()
+
+    state = hass.states.get(FAN_GROUP)
+    assert state.attributes.get(ATTR_ASSUMED_STATE) is True
+
+    # All members without assumed_state -> group doesn't have assumed_state in attributes
+    hass.states.async_set(LIVING_ROOM_FAN_ENTITY_ID, STATE_ON, {})
+    await hass.async_block_till_done()
+
+    state = hass.states.get(FAN_GROUP)
+    assert ATTR_ASSUMED_STATE not in state.attributes
diff --git a/tests/components/group/test_light.py b/tests/components/group/test_light.py
index dbd74e957806..a8fbe50970ce 100644
--- a/tests/components/group/test_light.py
+++ b/tests/components/group/test_light.py
@@ -30,6 +30,7 @@ from homeassistant.components.light import (
     ColorMode,
 )
 from homeassistant.const import (
+    ATTR_ASSUMED_STATE,
     ATTR_ENTITY_ID,
     ATTR_SUPPORTED_FEATURES,
     EVENT_CALL_SERVICE,
@@ -1647,3 +1648,72 @@ async def test_nested_group(hass: HomeAssistant) -> None:
     assert hass.states.get("light.kitchen_lights").state == STATE_OFF
     assert hass.states.get("light.bedroom_group").state == STATE_OFF
     assert hass.states.get("light.nested_group").state == STATE_OFF
+
+
+async def test_assumed_state(hass: HomeAssistant) -> None:
+    """Test assumed_state attribute behavior."""
+    await async_setup_component(
+        hass,
+        LIGHT_DOMAIN,
+        {
+            LIGHT_DOMAIN: {
+                "platform": DOMAIN,
+                "entities": ["light.kitchen", "light.bedroom", "light.living_room"],
+                "name": "Light Group",
+            }
+        },
+    )
+    await hass.async_block_till_done()
+    await hass.async_start()
+    await hass.async_block_till_done()
+
+    # No members with assumed_state -> group doesn't have assumed_state in attributes
+    hass.states.async_set("light.kitchen", STATE_ON, {})
+    hass.states.async_set("light.bedroom", STATE_ON, {})
+    hass.states.async_set("light.living_room", STATE_OFF, {})
+    await hass.async_block_till_done()
+
+    state = hass.states.get("light.light_group")
+    assert ATTR_ASSUMED_STATE not in state.attributes
+
+    # One member with assumed_state=True -> group has assumed_state=True
+    hass.states.async_set("light.kitchen", STATE_ON, {ATTR_ASSUMED_STATE: True})
+    await hass.async_block_till_done()
+
+    state = hass.states.get("light.light_group")
+    assert state.attributes.get(ATTR_ASSUMED_STATE) is True
+
+    # Multiple members with assumed_state=True -> group has assumed_state=True
+    hass.states.async_set("light.bedroom", STATE_OFF, {ATTR_ASSUMED_STATE: True})
+    hass.states.async_set("light.living_room", STATE_OFF, {ATTR_ASSUMED_STATE: True})
+    await hass.async_block_till_done()
+
+    state = hass.states.get("light.light_group")
+    assert state.attributes.get(ATTR_ASSUMED_STATE) is True
+
+    # Unavailable member with assumed_state=True -> group has assumed_state=True
+    hass.states.async_set("light.kitchen", STATE_ON, {})
+    hass.states.async_set("light.bedroom", STATE_OFF, {})
+    hass.states.async_set(
+        "light.living_room", STATE_UNAVAILABLE, {ATTR_ASSUMED_STATE: True}
+    )
+    await hass.async_block_till_done()
+
+    state = hass.states.get("light.light_group")
+    assert state.attributes.get(ATTR_ASSUMED_STATE) is True
+
+    # Unknown member with assumed_state=True -> group has assumed_state=True
+    hass.states.async_set(
+        "light.living_room", STATE_UNKNOWN, {ATTR_ASSUMED_STATE: True}
+    )
+    await hass.async_block_till_done()
+
+    state = hass.states.get("light.light_group")
+    assert state.attributes.get(ATTR_ASSUMED_STATE) is True
+
+    # All members without assumed_state -> group doesn't have assumed_state in attributes
+    hass.states.async_set("light.living_room", STATE_OFF, {})
+    await hass.async_block_till_done()
+
+    state = hass.states.get("light.light_group")
+    assert ATTR_ASSUMED_STATE not in state.attributes
diff --git a/tests/components/group/test_switch.py b/tests/components/group/test_switch.py
index 4230a6ee86fb..b577d2a6e2b2 100644
--- a/tests/components/group/test_switch.py
+++ b/tests/components/group/test_switch.py
@@ -14,6 +14,7 @@ from homeassistant.components.switch import (
     SERVICE_TURN_ON,
 )
 from homeassistant.const import (
+    ATTR_ASSUMED_STATE,
     ATTR_ENTITY_ID,
     STATE_OFF,
     STATE_ON,
@@ -458,3 +459,43 @@ async def test_nested_group(hass: HomeAssistant) -> None:
     assert hass.states.get("switch.decorative_lights").state == STATE_OFF
     assert hass.states.get("switch.some_group").state == STATE_OFF
     assert hass.states.get("switch.nested_group").state == STATE_OFF
+
+
+async def test_assumed_state(hass: HomeAssistant) -> None:
+    """Test assumed_state attribute behavior."""
+    await async_setup_component(
+        hass,
+        SWITCH_DOMAIN,
+        {
+            SWITCH_DOMAIN: {
+                "platform": DOMAIN,
+                "entities": ["switch.tv", "switch.soundbar"],
+                "name": "Media Group",
+            }
+        },
+    )
+    await hass.async_block_till_done()
+    await hass.async_start()
+    await hass.async_block_till_done()
+
+    # No members with assumed_state -> group doesn't have assumed_state in attributes
+    hass.states.async_set("switch.tv", STATE_ON, {})
+    hass.states.async_set("switch.soundbar", STATE_OFF, {})
+    await hass.async_block_till_done()
+
+    state = hass.states.get("switch.media_group")
+    assert ATTR_ASSUMED_STATE not in state.attributes
+
+    # One member with assumed_state=True -> group has assumed_state=True
+    hass.states.async_set("switch.tv", STATE_ON, {ATTR_ASSUMED_STATE: True})
+    await hass.async_block_till_done()
+
+    state = hass.states.get("switch.media_group")
+    assert state.attributes.get(ATTR_ASSUMED_STATE) is True
+
+    # All members without assumed_state -> group doesn't have assumed_state in attributes
+    hass.states.async_set("switch.tv", STATE_ON, {})
+    await hass.async_block_till_done()
+
+    state = hass.states.get("switch.media_group")
+    assert ATTR_ASSUMED_STATE not in state.attributes