diff --git a/stable/prometheus/README.md b/stable/prometheus/README.md
index 0282c50476..c9eac5ff95 100644
--- a/stable/prometheus/README.md
+++ b/stable/prometheus/README.md
@@ -303,7 +303,7 @@ Parameter | Description | Default
 `serviceAccounts.server.create` | If true, create the server service account | `true`
 `serviceAccounts.server.name` | name of the server service account to use or create | `{{ prometheus.server.fullname }}`
 `server.terminationGracePeriodSeconds` | Prometheus server Pod termination grace period | `300`
-`server.retention` | (optional) Prometheus data retention | `""`
+`server.retention` | (optional) Prometheus data retention | `"15d"`
 `serverFiles.alerts` | Prometheus server alerts configuration | `{}`
 `serverFiles.rules` | Prometheus server rules configuration | `{}`
 `serverFiles.prometheus.yml` | Prometheus server scrape configuration | example configuration
diff --git a/stable/prometheus/values.yaml b/stable/prometheus/values.yaml
index 094980ca0c..8fbc4d436c 100644
--- a/stable/prometheus/values.yaml
+++ b/stable/prometheus/values.yaml
@@ -778,9 +778,9 @@ server:
   ##
   terminationGracePeriodSeconds: 300
 
-  ## Prometheus data retention period (i.e 360h)
+  ## Prometheus data retention period (default if not specified is 15 days)
   ##
-  retention: ""
+  retention: "15d"
 
 pushgateway:
   ## If false, pushgateway will not be installed