diff --git a/source/docs/str/isalpha.rst b/source/docs/str/isalpha.rst
index 7575864..789c611 100644
--- a/source/docs/str/isalpha.rst
+++ b/source/docs/str/isalpha.rst
@@ -16,7 +16,7 @@ Return Value
 
 Time Complexity
 ---------------
-#TODO
+O(1)
 
 Remarks
 -------