diff --git a/kasa/device.py b/kasa/device.py
@@ -435,7 +435,11 @@ def has_emeter(self) -> bool:
     @property
     @abstractmethod
     def on_since(self) -> datetime | None:
-        """Return the time that the device was turned on or None if turned off."""
+        """Return the time that the device was turned on or None if turned off.
+
+        This returns a cached value if the device reported value difference is under
+        five seconds to avoid device-caused jitter.
+        """
 
     @abstractmethod
     async def wifi_scan(self) -> list[WifiNetwork]:

diff --git a/kasa/iot/iotdevice.py b/kasa/iot/iotdevice.py
@@ -181,6 +181,7 @@ def __init__(
         self._legacy_features: set[str] = set()
         self._children: Mapping[str, IotDevice] = {}
         self._modules: dict[str | ModuleName[Module], IotModule] = {}
+        self._on_since: datetime | None = None
 
     @property
     def children(self) -> Sequence[IotDevice]:
@@ -594,18 +595,25 @@ async def set_state(self, on: bool):
     @property  # type: ignore
     @requires_update
     def on_since(self) -> datetime | None:
-        """Return pretty-printed on-time, or None if not available."""
-        if "on_time" not in self._sys_info:
-            return None
+        """Return the time that the device was turned on or None if turned off.
 
-        if self.is_off:
+        This returns a cached value if the device reported value difference is under
+        five seconds to avoid device-caused jitter.
+        """
+        if self.is_off or "on_time" not in self._sys_info:
+            self._on_since = None
             return None
 
         on_time = self._sys_info["on_time"]
 
-        return datetime.now(timezone.utc).astimezone().replace(
-            microsecond=0
-        ) - timedelta(seconds=on_time)
+        time = datetime.now(timezone.utc).astimezone().replace(microsecond=0)
+
+        on_since = time - timedelta(seconds=on_time)
+        if not self._on_since or timedelta(
+            seconds=0
+        ) < on_since - self._on_since > timedelta(seconds=5):
+            self._on_since = on_since
+        return self._on_since
 
     @property  # type: ignore
     @requires_update

diff --git a/kasa/iot/iotstrip.py b/kasa/iot/iotstrip.py
@@ -318,6 +318,7 @@ def __init__(self, host: str, parent: IotStrip, child_id: str) -> None:
         self._set_sys_info(parent.sys_info)
         self._device_type = DeviceType.StripSocket
         self.protocol = parent.protocol  # Must use the same connection as the parent
+        self._on_since: datetime | None = None
 
     async def _initialize_modules(self):
         """Initialize modules not added in init."""
@@ -438,14 +439,20 @@ def next_action(self) -> dict:
     def on_since(self) -> datetime | None:
         """Return on-time, if available."""
         if self.is_off:
+            self._on_since = None
             return None
 
         info = self._get_child_info()
         on_time = info["on_time"]
 
-        return datetime.now(timezone.utc).astimezone().replace(
-            microsecond=0
-        ) - timedelta(seconds=on_time)
+        time = datetime.now(timezone.utc).astimezone().replace(microsecond=0)
+
+        on_since = time - timedelta(seconds=on_time)
+        if not self._on_since or timedelta(
+            seconds=0
+        ) < on_since - self._on_since > timedelta(seconds=5):
+            self._on_since = on_since
+        return self._on_since
 
     @property  # type: ignore
     @requires_update

diff --git a/kasa/smart/smartdevice.py b/kasa/smart/smartdevice.py
@@ -66,6 +66,7 @@ def __init__(
         self._children: Mapping[str, SmartDevice] = {}
         self._last_update = {}
         self._last_update_time: float | None = None
+        self._on_since: datetime | None = None
 
     async def _initialize_children(self):
         """Initialize children for power strips."""
@@ -494,15 +495,25 @@ def time(self) -> datetime:
 
     @property
     def on_since(self) -> datetime | None:
-        """Return the time that the device was turned on or None if turned off."""
+        """Return the time that the device was turned on or None if turned off.
+
+        This returns a cached value if the device reported value difference is under
+        five seconds to avoid device-caused jitter.
+        """
         if (
             not self._info.get("device_on")
             or (on_time := self._info.get("on_time")) is None
         ):
+            self._on_since = None
             return None
 
         on_time = cast(float, on_time)
-        return self.time - timedelta(seconds=on_time)
+        on_since = self.time - timedelta(seconds=on_time)
+        if not self._on_since or timedelta(
+            seconds=0
+        ) < on_since - self._on_since > timedelta(seconds=5):
+            self._on_since = on_since
+        return self._on_since
 
     @property
     def timezone(self) -> dict: