Timetate
A world clock on a live 3D globe. It reads your device's clock — which is exactly why the rest of this page matters.
Exact time is Coordinated Universal Time (UTC), shifted by your time zone's offset. UTC is calculated from hundreds of atomic clocks around the world and delivered to your device over the internet or a cellular network. A well-synced phone or computer is usually within a fraction of a second of it. An unsynced one can drift by seconds every day.
It means your clock agrees with the official international time scale, rather than with a clock someone set by hand. That scale is UTC, and every local time is UTC plus or minus an offset, with daylight saving applied in the places that still use it.
So two separate questions sit behind every “what time is it?” search. Is the reference correct? Almost always — it is maintained by international laboratories. Is your clock correct? That is where the errors are, because your device only matches the reference if it synchronises with it regularly.
Three layers: an atomic definition of the second, a worldwide average of atomic clocks, and national laboratories that broadcast real-time copies.
Since 1967 the SI second has been defined as exactly 9,192,631,770 oscillations of the hyperfine transition in caesium-133. Every caesium atom behaves identically, so any laboratory can reproduce the unit anywhere.
The best primary standards are extraordinarily precise. NIST reports that its newest fountain clock, NIST-F4, measures frequency to within 2.2 parts in 1016 — stable enough that it would be off by less than a second today had it started running 100 million years ago. They are also rare: fewer than 20 caesium fountains operate anywhere in the world.
No single clock defines world time. UTC rests on roughly 450 atomic clocks in 85 national time laboratories, which send their data to the International Bureau of Weights and Measures (BIPM) near Paris. The BIPM computes a weighted average of the designated clocks to produce International Atomic Time (TAI). UTC follows directly from it, running at the same rate and differing only by a whole number of accumulated leap seconds.
Because that averaging takes time, nobody's clock shows official UTC live. TAI and UTC are “paper” scales, computable only once every contributor's data has arrived. National laboratories keep real-time versions that come within a few nanoseconds of the final figure — in the United States, UTC, UTC(NIST) and UTC(USNO) agree to within 20 nanoseconds. That is the agreement behind time.gov and the time servers your devices use.
A site cannot put the time on your screen instantly, so a synchronised one measures the delay and corrects for it. Time.gov documents the method openly: the browser checks your local clock, requests a timestamp from a NIST server, then checks your clock again when the reply lands. The difference is the round trip, and half of it is assumed to have happened in each direction. Done properly, this lands within tenths of a second.
When you judge any web clock, look for two things: a stated source, and a displayed offset or network delay. Their absence is what separates a synchronised clock from a page quietly repeating your own device's time back to you. Plenty of well-known clocks describe themselves as showing “official atomic clock time” while publishing neither.
What Timetate's own clock does
By the standard set above: Timetate reads your device's clock and re-renders it once a second. It does not contact a time server, so it does not correct for drift and cannot be more accurate than the machine you are reading it on. If your device is ten seconds fast, so are we.
What Timetate is built for is the relationship between clocks — offsets, day and night, daylight saving, and the hours two cities have in common — where a second's drift changes nothing. For the absolute reading, check time.gov and sync your device using the steps below.
Only as accurate as its last synchronisation, because the hardware underneath is inexpensive. Left alone, computer clocks can lose several seconds a day. Phones set themselves periodically from the nearest cellular base station; computers rely on internet time servers, which most operating systems poll automatically over the Network Time Protocol (NTP) whenever the device is online.
In practice a connected device with automatic time enabled sits within a second of UTC. It drifts noticeably in four situations: automatic time is switched off, the device has been offline for days, a virtual machine or dual-boot setup is fighting the system clock, or a corporate network blocks NTP traffic.
Turning on automatic time and forcing one sync fixes nearly every drift problem. Under a minute on each platform.
Settings → Time & language → Date & time. Turn on Set time automatically, then click Sync now. Right-clicking the system clock and choosing to sync does the same thing.
System Settings → General → Date & Time. Turn on Set time and date automatically and leave the default Apple time server selected.
Settings → General → Date & Time, then turn on Set Automatically. If the switch is greyed out, check Screen Time restrictions or a device-management profile.
Settings → System → Date & time. Turn on both Set time automatically and Set time zone automatically. Menu names vary slightly by manufacturer.
Open time.gov and compare. If the gap still exceeds a second after syncing, check whether your network blocks time servers on UDP port 123, and whether a VPN is shifting your detected location.
Your device needs the right time zone as well as the right UTC. A perfectly synced clock in the wrong zone is wrong by a whole number of hours — which is why automatic time zone detection matters as much as automatic time.
Daylight saving is the second trap. In 2026 the clocks go back on 25 October across most of Europe and the UK, and on 1 November in the United States and Canada. For that week in between, transatlantic differences are an hour off their usual value. The 2026 clock-change dates list every country, and you can convert time between cities with the shift already applied for the date you pick.
Leap seconds exist because Earth's rotation is irregular and atomic time is not. When the gap between UTC and Earth-rotation time approaches 0.9 seconds, a leap second is announced and applied everywhere at once. The first was inserted on 30 June 1972; 27 have been added since, most recently on 31 December 2016, which is why TAI now runs 37 seconds ahead of UTC.
That system is being retired. In November 2022 the General Conference on Weights and Measures (CGPM) adopted a plan to phase out future leap seconds by or before 2035, and the 28th CGPM meets on 13–15 October 2026 in Versailles to decide the mechanism. Reporting on the draft resolution describes a much wider tolerance between atomic and Earth-rotation time, taking effect later this decade — but the specifics are not settled until that vote, and we are not going to state them as though they were.
For everyday use the practical effect is simple either way: no more one-second glitches in logs, trading systems and navigation software.
| Source | What it gives you | Best for |
|---|---|---|
| time.gov (NIST/USNO) | UTC(NIST), corrected for measured network delay | The official US reference, and checking your device against it |
| A branded web clock | A reading for many cities and languages | Quick lookups — check whether it states its source |
| Your OS time sync (NTP) | Automatic, periodic correction against internet time servers | Keeping every app and timestamp on the machine right |
| Phone network time | Set from the nearest cellular base station | Mobile devices on the move |
Planning across zones rather than checking one? The meeting planner shows the hours your cities actually have in common.
Last updated . Clocks on this page update live in your browser.