diff --git a/homeassistant/components/opower/sensor.py b/homeassistant/components/opower/sensor.py
index f9d0fe62332..18518c9e21e 100644
--- a/homeassistant/components/opower/sensor.py
+++ b/homeassistant/components/opower/sensor.py
@@ -4,6 +4,7 @@ from __future__ import annotations
 
 from collections.abc import Callable
 from dataclasses import dataclass
+from datetime import date
 
 from opower import Forecast, MeterType, UnitOfMeasure
 
@@ -29,7 +30,7 @@ from .coordinator import OpowerCoordinator
 class OpowerEntityDescription(SensorEntityDescription):
     """Class describing Opower sensors entities."""
 
-    value_fn: Callable[[Forecast], str | float]
+    value_fn: Callable[[Forecast], str | float | date]
 
 
 # suggested_display_precision=0 for all sensors since
@@ -97,7 +98,7 @@ ELEC_SENSORS: tuple[OpowerEntityDescription, ...] = (
         device_class=SensorDeviceClass.DATE,
         entity_category=EntityCategory.DIAGNOSTIC,
         entity_registry_enabled_default=False,
-        value_fn=lambda data: str(data.start_date),
+        value_fn=lambda data: data.start_date,
     ),
     OpowerEntityDescription(
         key="elec_end_date",
@@ -105,7 +106,7 @@ ELEC_SENSORS: tuple[OpowerEntityDescription, ...] = (
         device_class=SensorDeviceClass.DATE,
         entity_category=EntityCategory.DIAGNOSTIC,
         entity_registry_enabled_default=False,
-        value_fn=lambda data: str(data.end_date),
+        value_fn=lambda data: data.end_date,
     ),
 )
 GAS_SENSORS: tuple[OpowerEntityDescription, ...] = (
@@ -169,7 +170,7 @@ GAS_SENSORS: tuple[OpowerEntityDescription, ...] = (
         device_class=SensorDeviceClass.DATE,
         entity_category=EntityCategory.DIAGNOSTIC,
         entity_registry_enabled_default=False,
-        value_fn=lambda data: str(data.start_date),
+        value_fn=lambda data: data.start_date,
     ),
     OpowerEntityDescription(
         key="gas_end_date",
@@ -177,7 +178,7 @@ GAS_SENSORS: tuple[OpowerEntityDescription, ...] = (
         device_class=SensorDeviceClass.DATE,
         entity_category=EntityCategory.DIAGNOSTIC,
         entity_registry_enabled_default=False,
-        value_fn=lambda data: str(data.end_date),
+        value_fn=lambda data: data.end_date,
     ),
 )
 
@@ -247,7 +248,7 @@ class OpowerSensor(CoordinatorEntity[OpowerCoordinator], SensorEntity):
         self.utility_account_id = utility_account_id
 
     @property
-    def native_value(self) -> StateType:
+    def native_value(self) -> StateType | date:
         """Return the state."""
         if self.coordinator.data is not None:
             return self.entity_description.value_fn(