diff --git a/moto/cloudwatch/models.py b/moto/cloudwatch/models.py
index 3bd509b25..d81d1ae48 100644
--- a/moto/cloudwatch/models.py
+++ b/moto/cloudwatch/models.py
@@ -500,7 +500,7 @@ class CloudWatchBackend(BaseBackend):
     ) -> List[Dict[str, Any]]:
 
         period_data = [
-            md for md in self.metric_data if start_time <= md.timestamp <= end_time
+            md for md in self.metric_data if start_time <= md.timestamp < end_time
         ]
 
         results = []
@@ -582,7 +582,7 @@ class CloudWatchBackend(BaseBackend):
             for md in self.get_all_metrics()
             if md.namespace == namespace
             and md.name == metric_name
-            and start_time <= md.timestamp <= end_time
+            and start_time <= md.timestamp < end_time
         ]
 
         if unit: