diff --git a/index.js b/index.js
index <HASH>..<HASH> 100644
--- a/index.js
+++ b/index.js
@@ -25,12 +25,14 @@ module.exports = function responseTime(){
   return function(req, res, next){
     next = next || noop;
     if (res._responseTime) return next();
-    var start = Date.now();
     res._responseTime = true;
 
+    var startAt = process.hrtime()
+
     onHeaders(res, function () {
-      var duration = Date.now() - start
-      this.setHeader('X-Response-Time', duration + 'ms')
+      var diff = process.hrtime(startAt)
+      var ms = diff[0] * 1e3 + diff[1] * 1e-6
+      this.setHeader('X-Response-Time', ms.toFixed(3) + 'ms')
     })
 
     next();
make timer immune to clock drift and more precise