diff --git a/docs/datetime.rst b/docs/datetime.rst
index ba846c4..f718881 100644
--- a/docs/datetime.rst
+++ b/docs/datetime.rst
@@ -13,5 +13,12 @@ Snippets about datetime.
 
     date_object = datetime.strptime('Jun 1 2005  1:33PM', '%b %d %Y %I:%M%p')
 
+    """
+    年份差计算
+    """
+    age = gmtime()[0] - self.birth_date.year
+    if gmtime()[1] >= self.birth_date.month:
+        age += 1
+    return age
 
 .. _converting string into datetime: http://stackoverflow.com/questions/466345/converting-string-into-datetime