diff --git a/source/reference/operator/aggregation/subtract.txt b/source/reference/operator/aggregation/subtract.txt
index da8d3737875..6eb48b826bf 100644
--- a/source/reference/operator/aggregation/subtract.txt
+++ b/source/reference/operator/aggregation/subtract.txt
@@ -65,7 +65,8 @@ Subtract Two Dates
 ~~~~~~~~~~~~~~~~~~
 
 The following aggregation uses the :expression:`$subtract` expression
-to subtract ``$date`` from the current date:
+to subtract ``$date`` from the current date and returns the difference 
+in milliseconds:
 
 .. code-block:: javascript