Date.now() // 1337376068250 performance.now() // 20303.427000007 You'll notice the two above values are many orders of magnitude different. performance.now() is a measurement of floating point milliseconds since that particular page started to load (the performance.timing.[navigationStart](https://www.w3.org/TR/navigation-timing/#dom-performancetiming-navigationstart) timeStamp to be specific). Yo