atomicclock Atomic clock now

Current UTC Time

Coordinated Universal Time to the millisecond, referenced to a synchronised server.

Coordinated Universal Time is the reference every civil clock in the world is defined against. The display above is corrected by the measured offset between your device and the server, so it is closer to true UTC than your own clock would be.

UTC is a compromise between two clocks

Atomic clocks keep a perfectly steady second; the Earth's rotation does not. UTC follows the atomic second but has historically been nudged with leap seconds to stay within 0.9 seconds of the Earth's actual rotation. That compromise, and the decision to end it, is covered in leap seconds explained.

UTC, GMT and TAI

GMT is the older astronomical term and is close enough for everyday use. TAI is pure atomic time with no leap seconds, and runs a fixed number of seconds ahead of UTC. GPS time is a third scale again. The three are compared live on the TAI page.

Guides about UTC Time

The science Leap Seconds Explained: Why the Clock Sometimes Says 23:59:60 Why Earth's rotation forces the occasional leap second, who decides when one is inserted, the problems it causes for computers, and why the practice is being abandoned by 2035. 5 min read The science National Time Standards: NIST Time and Its Counterparts What national metrology institutes such as NIST, NPL and PTB actually do, how their atomic clocks are combined into International Atomic Time by the BIPM, and how the public gets that time. 5 min read

More atomicclock.now pages

Atomic Clock Now Server-referenced time, and how far your own device clock is from it — measured live in milliseconds. Clock Sync Check Measure your device's clock against a reference and get a plain verdict — plus how to fix it. TAI vs UTC vs GPS Three time scales, side by side, with the fixed offsets between them.

Frequently asked questions

What is UTC?
Coordinated Universal Time, the global reference against which every time zone is defined. It does not change for daylight saving.
Is UTC the same as GMT?
For everyday purposes yes. UTC is the modern atomic standard and GMT is the older astronomical term for essentially the same reference.
How precise is this UTC display?
It corrects your device's clock by the measured server offset, which is typically good to a few tens of milliseconds.