diff --git a/pkg/services/alerting/eval_context.go b/pkg/services/alerting/eval_context.go
index e4b3a8a2fbf..c67804c163c 100644
--- a/pkg/services/alerting/eval_context.go
+++ b/pkg/services/alerting/eval_context.go
@@ -107,7 +107,7 @@ func (c *EvalContext) shouldUpdateAlertState() bool {
 
 // GetDurationMs returns the duration of the alert evaluation.
 func (c *EvalContext) GetDurationMs() float64 {
-	return float64(c.EndTime.Nanosecond()-c.StartTime.Nanosecond()) / float64(1000000)
+	return float64(c.EndTime.Sub(c.StartTime).Nanoseconds()) / float64(time.Millisecond)
 }
 
 // GetNotificationTitle returns the title of the alert rule including alert state.
diff --git a/pkg/services/alerting/eval_context_test.go b/pkg/services/alerting/eval_context_test.go
index d05ea3b995c..b731ed3542c 100644
--- a/pkg/services/alerting/eval_context_test.go
+++ b/pkg/services/alerting/eval_context_test.go
@@ -404,3 +404,18 @@ func TestEvaluateNotificationTemplateFields(t *testing.T) {
 		})
 	}
 }
+
+func TestGetDurationFromEvalContext(t *testing.T) {
+	startTime, err := time.Parse("2006-01-02 15:04:05.999999999 -0700 MST", "2022-10-03 11:33:14.438803 +0200 CEST")
+	require.NoError(t, err)
+
+	endTime, err := time.Parse("2006-01-02 15:04:05.999999999 -0700 MST", "2022-10-03 11:33:15.291075 +0200 CEST")
+	require.NoError(t, err)
+
+	evalContext := EvalContext{
+		StartTime: startTime,
+		EndTime:   endTime,
+	}
+
+	assert.Equal(t, float64(852.272), evalContext.GetDurationMs())
+}