diff --git a/src/data/timer.ts b/src/data/timer.ts
index 4b0ab1ce2768..3290be645d7d 100644
--- a/src/data/timer.ts
+++ b/src/data/timer.ts
@@ -72,8 +72,8 @@ export const timerTimeRemaining = (
 
   if (stateObj.state === "active") {
     const now = new Date().getTime();
-    const madeActive = new Date(stateObj.last_changed).getTime();
-    timeRemaining = Math.max(timeRemaining - (now - madeActive) / 1000, 0);
+    const finishes = new Date(stateObj.attributes.finishes_at).getTime();
+    timeRemaining = Math.max((finishes - now) / 1000, 0);
   }
 
   return timeRemaining;
diff --git a/test/common/entity/timer_time_remaining_test.ts b/test/common/entity/timer_time_remaining_test.ts
index 13ba7eb20673..810f0e0f276a 100644
--- a/test/common/entity/timer_time_remaining_test.ts
+++ b/test/common/entity/timer_time_remaining_test.ts
@@ -42,8 +42,8 @@ describe("timerTimeRemaining", () => {
           state: "active",
           attributes: {
             remaining: "0:01:05",
+            finishes_at: "2018-01-17T16:16:17+00:00",
           },
-          last_changed: "2018-01-17T16:15:12Z",
         } as any),
         47
       );