diff --git a/app/dao/notifications_dao.py b/app/dao/notifications_dao.py
index b7047c989..85949dee9 100644
--- a/app/dao/notifications_dao.py
+++ b/app/dao/notifications_dao.py
@@ -47,7 +47,6 @@ from app.models import (
     Notification,
     NotificationHistory,
     ProviderDetails,
-    Service,
     ServiceDataRetention,
 )
 from app.utils import (
@@ -323,16 +322,31 @@ def delete_notifications_older_than_retention_by_type(notification_type, qry_lim
         deleted += _move_notifications_to_notification_history(
             notification_type, f.service_id, day_to_delete_backwards_from, qry_limit)
 
-    current_app.logger.info(
-        'Deleting {} notifications for services without flexible data retention'.format(notification_type))
-
     seven_days_ago = get_london_midnight_in_utc(convert_utc_to_bst(datetime.utcnow()).date()) - timedelta(days=7)
-    services_with_data_retention = [x.service_id for x in flexible_data_retention]
-    service_ids_to_purge = Service.query.filter(Service.id.notin_(services_with_data_retention)).all()
+    service_ids_with_data_retention = {x.service_id for x in flexible_data_retention}
 
-    for service in service_ids_to_purge:
+    # get a list of all service ids that we'll need to delete for. Typically that might only be 5% of services.
+    # This query takes a couple of mins to run.
+    service_ids_that_have_sent_notifications_recently = {
+        row.service_id
+        for row in db.session.query(
+            Notification.service_id
+        ).filter(
+            Notification.notification_type == notification_type,
+            Notification.created_at < seven_days_ago
+        ).distinct()
+    }
+
+    service_ids_to_purge = service_ids_that_have_sent_notifications_recently - service_ids_with_data_retention
+
+    current_app.logger.info('Deleting {} notifications for {} services without flexible data retention'.format(
+        notification_type,
+        len(service_ids_to_purge)
+    ))
+
+    for service_id in service_ids_to_purge:
         deleted += _move_notifications_to_notification_history(
-            notification_type, service.id, seven_days_ago, qry_limit)
+            notification_type, service_id, seven_days_ago, qry_limit)
 
     current_app.logger.info('Finished deleting {} notifications'.format(notification_type))
 
diff --git a/tests/app/dao/notification_dao/test_notification_dao_delete_notifications.py b/tests/app/dao/notification_dao/test_notification_dao_delete_notifications.py
index 808b15386..db83e31f8 100644
--- a/tests/app/dao/notification_dao/test_notification_dao_delete_notifications.py
+++ b/tests/app/dao/notification_dao/test_notification_dao_delete_notifications.py
@@ -1,4 +1,5 @@
 from datetime import date, datetime, timedelta
+from unittest.mock import ANY, call
 
 import boto3
 import pytest
@@ -446,3 +447,57 @@ def test_insert_notification_history_delete_notifications_insert_for_key_type(sa
     assert len(notifications) == 1
     assert with_test_key.id == notifications[0].id
     assert len(history_rows) == 2
+
+
+@freeze_time('2020-12-10')
+def test_delete_notifications_only_runs_move_notifications_for_services_that_have_things_to_delete(mocker):
+    move_notifications_mock = mocker.patch(
+        'app.dao.notifications_dao._move_notifications_to_notification_history',
+        return_value=0
+    )
+
+    service_retention_will_delete = create_service(service_name='a')
+    service_retention_nothing_to_delete = create_service(service_name='b')
+    service_will_delete = create_service(service_name='c')
+    service_nothing_to_delete = create_service(service_name='d')
+
+    create_service_data_retention(
+        service_retention_will_delete,
+        notification_type='sms',
+        days_of_retention=3
+    )
+    create_service_data_retention(
+        service_retention_nothing_to_delete,
+        notification_type='sms',
+        days_of_retention=3
+    )
+
+    create_template(service_retention_will_delete)
+    create_template(service_retention_nothing_to_delete)
+    create_template(service_will_delete)
+    nothing_to_delete_sms_template = create_template(service_nothing_to_delete, template_type='sms')
+    nothing_to_delete_email_template = create_template(service_nothing_to_delete, template_type='email')
+
+    # this notification will be deleted because it's past retention
+    create_notification(service_retention_will_delete.templates[0], created_at=datetime.now() - timedelta(days=8))
+
+    # will be deleted as service has no custom retention, but past our default 7 days
+    create_notification(service_will_delete.templates[0], created_at=datetime.now() - timedelta(days=8))
+
+    # will be kept as it's recent, but we'll still run _move_notifications_to_notification_history
+    # as it's for a service with custom retention
+    create_notification(service_retention_nothing_to_delete.templates[0], created_at=datetime.now() - timedelta(days=2))
+
+    # will be kept as it's recent, and we won't run _move_notifications_to_notification_history
+    create_notification(nothing_to_delete_sms_template, created_at=datetime.now() - timedelta(days=2))
+    # this is an old notification, but for email not sms, so we won't run _move_notifications_to_notification_history
+    create_notification(nothing_to_delete_email_template, created_at=datetime.now() - timedelta(days=2))
+
+    delete_notifications_older_than_retention_by_type('sms')
+
+    # called for all services except for "service_nothing_to_delete"
+    move_notifications_mock.assert_has_calls([
+        call('sms', service_retention_will_delete.id, ANY, ANY),
+        call('sms', service_retention_nothing_to_delete.id, ANY, ANY),
+        call('sms', service_will_delete.id, ANY, ANY),
+    ], any_order=True)