Exact Time — Check Your Clock
The precise time, and exactly how far off your own clock is.
Behind the exact time
The same instant, shown on the four time scales that run the modern world — live.
Leap seconds
Earth's spin is slightly irregular, so UTC is kept in step with the Sun using leap seconds: when UTC began in 1972 it already differed from TAI by 10 seconds, and 27 leap seconds have been inserted since. The last one was on 2017-01-01; none have been added since. That is why TAI is now exactly 37 seconds ahead of UTC.
Atomic clocks
TAI is the average of hundreds of caesium and other atomic clocks around the world. They count the natural vibration of atoms — 9,192,631,770 cycles define one second — and would drift by less than a second over millions of years.
How we measure your offset
Your browser asks our server for the time several times. For each request we measure the round-trip delay and assume it is split evenly between sending and receiving, then take the fastest exchange as the best estimate — the same idea NTP uses. We don't talk to an atomic clock directly; our server is itself synced over NTP.
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