How accurate is this clock?

Your device clock can drift by seconds or even minutes. Instead of trusting it, this page measures the time on our server several times, keeps the measurement with the shortest network round trip and corrects for half of that delay. The clock then advances using your browser’s monotonic timer, so it is not affected if your system clock jumps, and it resynchronizes automatically every few minutes and whenever you return to the tab.

The indicator under the clock shows how far your device clock is off and the worst-case error of the measurement (typically a few to a few dozen milliseconds). Our server is synchronized via NTP by its hosting provider; we do not claim atomic-clock accuracy. Time zone and daylight saving rules come from the IANA time zone database built into your browser. Learn more.