diff --git a/src/sentry/uptime/endpoints/validators.py b/src/sentry/uptime/endpoints/validators.py
index 28155b43ad5755..e64fa3e4b732f3 100644
--- a/src/sentry/uptime/endpoints/validators.py
+++ b/src/sentry/uptime/endpoints/validators.py
@@ -25,6 +25,7 @@
     MaxManualUptimeSubscriptionsReached,
     MaxUrlsForDomainReachedException,
     UptimeMonitorNoSeatAvailable,
+    check_uptime_subscription_limit,
     check_url_limits,
     create_uptime_detector,
     create_uptime_subscription,
@@ -202,6 +203,16 @@ class UptimeMonitorValidator(CamelSnakeSerializer):
     )
 
     def validate(self, attrs):
+        # When creating a new uptime monitor, check if we would exceed the organization limit
+        if not self.instance:
+            organization = self.context["organization"]
+            try:
+                check_uptime_subscription_limit(organization.id)
+            except MaxManualUptimeSubscriptionsReached:
+                raise serializers.ValidationError(
+                    f"You may have at most {MAX_MANUAL_SUBSCRIPTIONS_PER_ORG} uptime monitors per organization"
+                )
+
         headers = []
         method = "GET"
         body = None
@@ -246,34 +257,29 @@ def create(self, validated_data):
         method_headers_body = {
             k: v for k, v in validated_data.items() if k in {"method", "headers", "body"}
         }
-        try:
-            detector = create_uptime_detector(
-                project=self.context["project"],
-                environment=environment,
-                url=validated_data["url"],
-                interval_seconds=validated_data["interval_seconds"],
-                timeout_ms=validated_data["timeout_ms"],
-                name=validated_data["name"],
-                status=validated_data.get("status"),
-                mode=validated_data.get("mode", UptimeMonitorMode.MANUAL),
-                owner=validated_data.get("owner"),
-                trace_sampling=validated_data.get("trace_sampling", False),
-                recovery_threshold=validated_data["recovery_threshold"],
-                downtime_threshold=validated_data["downtime_threshold"],
-                **method_headers_body,
-            )
+        detector = create_uptime_detector(
+            project=self.context["project"],
+            environment=environment,
+            url=validated_data["url"],
+            interval_seconds=validated_data["interval_seconds"],
+            timeout_ms=validated_data["timeout_ms"],
+            name=validated_data["name"],
+            status=validated_data.get("status"),
+            mode=validated_data.get("mode", UptimeMonitorMode.MANUAL),
+            owner=validated_data.get("owner"),
+            trace_sampling=validated_data.get("trace_sampling", False),
+            recovery_threshold=validated_data["recovery_threshold"],
+            downtime_threshold=validated_data["downtime_threshold"],
+            **method_headers_body,
+        )
 
-            create_audit_entry(
-                request=self.context["request"],
-                organization=self.context["organization"],
-                target_object=detector.id,
-                event=audit_log.get_event_id("UPTIME_MONITOR_ADD"),
-                data=get_audit_log_data(detector),
-            )
-        except MaxManualUptimeSubscriptionsReached:
-            raise serializers.ValidationError(
-                f"You may have at most {MAX_MANUAL_SUBSCRIPTIONS_PER_ORG} uptime monitors per organization"
-            )
+        create_audit_entry(
+            request=self.context["request"],
+            organization=self.context["organization"],
+            target_object=detector.id,
+            event=audit_log.get_event_id("UPTIME_MONITOR_ADD"),
+            data=get_audit_log_data(detector),
+        )
 
         return detector
 
diff --git a/src/sentry/uptime/subscriptions/subscriptions.py b/src/sentry/uptime/subscriptions/subscriptions.py
index d61d14549a53a1..87d3d7295dfa12 100644
--- a/src/sentry/uptime/subscriptions/subscriptions.py
+++ b/src/sentry/uptime/subscriptions/subscriptions.py
@@ -86,6 +86,22 @@ class MaxManualUptimeSubscriptionsReached(ValueError):
     pass
 
 
+def check_uptime_subscription_limit(organization_id: int) -> None:
+    """
+    Check if adding a new manual uptime monitor would exceed the organization's limit.
+    Raises MaxManualUptimeSubscriptionsReached if the limit would be exceeded.
+    """
+    manual_subscription_count = Detector.objects.filter(
+        status=ObjectStatus.ACTIVE,
+        type=GROUP_TYPE_UPTIME_DOMAIN_CHECK_FAILURE,
+        project__organization_id=organization_id,
+        config__mode=UptimeMonitorMode.MANUAL,
+    ).count()
+
+    if manual_subscription_count >= MAX_MANUAL_SUBSCRIPTIONS_PER_ORG:
+        raise MaxManualUptimeSubscriptionsReached
+
+
 class UptimeMonitorNoSeatAvailable(Exception):
     """
     Indicates that the quotes system is unable to allocate a seat for the new
@@ -234,13 +250,6 @@ def create_uptime_detector(
     Creates an UptimeSubscription and associated Detector
     """
     if mode == UptimeMonitorMode.MANUAL:
-        manual_subscription_count = Detector.objects.filter(
-            status=ObjectStatus.ACTIVE,
-            type=GROUP_TYPE_UPTIME_DOMAIN_CHECK_FAILURE,
-            project__organization=project.organization,
-            config__mode=UptimeMonitorMode.MANUAL,
-        ).count()
-
         # Once a user has created a subscription manually, make sure we disable all autodetection, and remove any
         # onboarding monitors
         if project.organization.get_option("sentry:uptime_autodetection", False):
@@ -250,11 +259,8 @@ def create_uptime_detector(
             ):
                 delete_uptime_detector(detector)
 
-        if (
-            not override_manual_org_limit
-            and manual_subscription_count >= MAX_MANUAL_SUBSCRIPTIONS_PER_ORG
-        ):
-            raise MaxManualUptimeSubscriptionsReached
+        if not override_manual_org_limit:
+            check_uptime_subscription_limit(project.organization_id)
 
     with atomic_transaction(
         using=(