Home › Date & Time
Your device clock drifts — most are off by a second or more. This clock checks a time server, measures how far your device is off, and corrects for it, so the time below tracks the official atomic time as closely as a web browser can.
| UTC time | — |
| Your time zone | — |
| Day of the year | — |
| ISO week number | — |
| Unix timestamp | — |
| Your device clock is | — |
The clock re-synchronizes every minute. Network delays limit any web clock: expect accuracy within a few dozen milliseconds on a good connection.
No clock in a browser is atomic by itself — your phone or computer keeps time with a quartz oscillator and drifts. What this page does is the next best thing: it asks a time server (itself synchronized to atomic clocks) what time it is, corrects for the network delay, and measures how far your device clock is off.
How the correction works. Suppose the page sends a request and your device clock reads 12:00:00.000. The server replies "12:00:00.500", and the reply arrives when your device reads 12:00:00.040. The trip took 40 ms, so the server's timestamp was about 20 ms old on arrival: the true time at arrival was 12:00:00.520. Your device said 12:00:00.040 at that moment, so it is running 480 ms slow — and this page adds 480 ms to everything it shows. The measurement repeats every minute.
The reference itself: UTC, the world's time standard, is computed by the Bureau International des Poids et Mesures from roughly 400 atomic clocks in laboratories around the world. Time servers distribute that standard; your device, corrected against one, is typically accurate to a few dozen milliseconds — the network, not the clock, is the limit.
An atomic clock counts the vibrations of atoms — cesium-133 atoms oscillate exactly 9,192,631,770 times per second, and that oscillation defines the second. The best atomic clocks gain or lose less than a second in millions of years. National laboratories run them to produce UTC, the time standard every country uses.
As right as a web page can make it. The page synchronizes to a time server fed by atomic-clock time and corrects for network delay. On a typical connection the display is within a few dozen milliseconds of true UTC — far better than an uncorrected device clock, which is often off by a second or more. If the time server cannot be reached, the page says so and shows your device clock uncorrected.
For everyday purposes, none: they agree to within a second. GMT is the older standard based on the Sun’s position over Greenwich, London. UTC replaced it as the world standard in 1972 and is kept by atomic clocks, with occasional leap seconds added to stay in step with Earth’s slightly irregular rotation.
Because synchronization is the point. At one-second resolution almost any clock looks right; the milliseconds show the correction working and make small offsets visible. If you are timing anything — a photo finish, a telescope event, a radio contact — the tenths and hundredths are where device drift shows up.
The count of seconds since 00:00:00 UTC on 1 January 1970, the "epoch" most computers use internally. It is shown live under the clock. Programmers use it to store and compare times without time-zone confusion.