diff --git a/app.py b/app.py
index 2410ef5..0679538 100644
--- a/app.py
+++ b/app.py
@@ -113,7 +113,7 @@
         ---
         ### See also
 
-        [Sample size calculator](http://samplesize.rfoxdata.co.uk/)
+        [Sample size calculator](https://abtestsamplesize.herokuapp.com/)
 
         ### Recommended Reading