diff --git a/modules/storage/aws-backup/main.tf b/modules/storage/aws-backup/main.tf
index 0b92017..0a6b982 100644
--- a/modules/storage/aws-backup/main.tf
+++ b/modules/storage/aws-backup/main.tf
@@ -117,7 +117,8 @@ resource "aws_backup_plan" "ab-plan" {
     }
   }
 
-  # monthly backup (takes precedence than daily)
+  # monthly backup (when overlap with daily, only monthly backup will be created.
+  # see https://docs.aws.amazon.com/aws-backup/latest/devguide/creating-a-backup-plan.html)
   rule {
     rule_name         = "Monthly"
     target_vault_name = each.value.name
@@ -127,6 +128,7 @@ resource "aws_backup_plan" "ab-plan" {
 
     lifecycle {
       delete_after = var.monthly-backup-retention
+      cold_storage_after = var.daily-backup-retention # move to cold storage after daily retention
     }
 
     recovery_point_tags = {