diff --git a/azurerm/internal/services/applicationinsights/application_insights_resource.go b/azurerm/internal/services/applicationinsights/application_insights_resource.go
index 7bc4a04b0de4..d595590506be 100644
--- a/azurerm/internal/services/applicationinsights/application_insights_resource.go
+++ b/azurerm/internal/services/applicationinsights/application_insights_resource.go
@@ -64,6 +64,7 @@ func resourceArmApplicationInsights() *schema.Resource {
 			"retention_in_days": {
 				Type:     schema.TypeInt,
 				Optional: true,
+				Default:  90,
 				ValidateFunc: validation.IntInSlice([]int{
 					30,
 					60,
diff --git a/website/docs/r/application_insights.html.markdown b/website/docs/r/application_insights.html.markdown
index 8bdbd7103347..87903dd273fd 100644
--- a/website/docs/r/application_insights.html.markdown
+++ b/website/docs/r/application_insights.html.markdown
@@ -52,7 +52,7 @@ The following arguments are supported:
 
 * `daily_data_cap_notifications_disabled` - (Optional) Specifies if a notification email will be send when the daily data volume cap is met.
 
-* `retention_in_days` - (Optional) Specifies the retention period in days. Possible values are `30`, `60`, `90`, `120`, `180`, `270`, `365`, `550` or `730`.
+* `retention_in_days` - (Optional) Specifies the retention period in days. Possible values are `30`, `60`, `90`, `120`, `180`, `270`, `365`, `550` or `730`. Defaults to `90`.
 
 * `sampling_percentage` - (Optional) Specifies the percentage of the data produced by the monitored application that is sampled for Application Insights telemetry.