diff --git a/back-out.js b/back-out.js
index 5484466..b2d9846 100644
--- a/back-out.js
+++ b/back-out.js
@@ -1,6 +1,6 @@
 function backOut(t) {
-  var s = 1.70158
-  return --t * t * ((s + 1) * t + s) + 1
+  var f = 1 - t;
+  return 1 - (Math.pow(f, 3) - f * Math.sin(f * Math.PI))
 }
 
-module.exports = backOut
\ No newline at end of file
+module.exports = backOut