Is your clock right?
Digital Clock Online compares your device clock with its server and shows the difference in seconds, together with the round trip the comparison rode on.
A clock that is seconds out has usually stopped correcting itself. The sections below explain what the figure means, why clocks drift, and how your device fixes its own clock when it is allowed to.
Checking your clock against the server.
How this check works
Your browser sends 3 requests to this site's time endpoint at once and times each one.
The reply with the shortest round trip wins. The server's time is taken to be halfway through that request, so half the round trip is the delay the result allows for.
The gap between that server time and your device clock is the figure above. Every clock on this site adds the same gap to your device clock, so the digits you see are server time even when your device is wrong.
The site checks again every 15 minutes, when you come back to the tab after 60 seconds away, and when your connection returns. The Check again button repeats the full measurement.
The same measurement runs behind the clock on the home page and behind every country and time zone page.
What the difference can and cannot tell you
The comparison travels over the internet, so it carries the network's uncertainty.
Time servers assume the answer took as long to come back as the question took to arrive. When the two directions differ, the error can be as large as half the round trip. With a round trip of 100 milliseconds, the uncertainty is at least a few milliseconds.
NIST, the US standards institute, says the accuracy a user sees from an internet time server depends mostly on how stable and how symmetrical the connection is.
So this check tells you whether your clock is seconds out, which is the error that matters for an exam hall, a trading desk or a train. It cannot tell you about milliseconds, and it does not claim to.
The server is this site's own server, hosted by Vercel. It is not an atomic clock, and the site does not present its time as authoritative. A difference of more than 5 seconds is treated as a device clock that needs attention, and the clock pages show a warning.
Why clocks drift
Nearly every computer and phone keeps time with a quartz crystal. Its frequency moves with temperature, humidity, pressure and vibration, and it changes as the crystal ages.
NIST calls that slow change in an oscillator's frequency drift. A clock running on a drifting oscillator gains or loses time until something corrects it, and the error keeps growing until then.
A NIST paper from the 1990s measured the hardware clocks in the personal computers of that time at 5 to 15 seconds of error a day, with 10 seconds typical. The crystals in today's devices are the same kind of part. What has changed is how often the device corrects itself.
The time shown on this site does not depend on your device's drift, because the gap to the server is measured again and again. The warning appears when your device clock has moved far from the server's.
How your device corrects itself
Operating systems correct the clock with the Network Time Protocol, NTP, the standard the internet uses to synchronise computer clocks. Windows, macOS and Linux can all do it automatically in the background.
Windows PCs that are not part of a company network take their time from time.windows.com by default. Microsoft says it cannot guarantee the accuracy of a computer with an intermittent connection or none.
Apple devices set their time from time.apple.com when Set Time Automatically is on, under Settings, General, Date and Time.
Android phones take time from NTP servers and from the mobile network's own time signal. Since Android 12 the network time comes first.
A clock that is minutes out has not been corrected. Check that automatic time is on and that the device has been online; the operating system does the rest. This site cannot set your clock for you.
When the time is right but the hour is wrong
A device can keep perfect time and still show the wrong hour, because the hour depends on time zone rules as well as the clock.
Those rules live in the IANA time zone database, which is updated when governments change their offsets or their daylight saving dates. Devices receive the updates from their software and operating system vendors.
Android ships the rules as a separate module that is applied after a restart. Windows carries them in its monthly updates. Apple devices may ask for a restart when updated time zone information arrives.
The clock pages on this site compare your browser's zone data with the database release the site is pinned to, and warn when the two disagree. The daylight saving dates page lists every clock change of the year.
Common questions
Why does the result change each time I check?
Each check travels over a changing network, so the round trip and the estimated server time move by a few milliseconds. A result that moves by milliseconds is normal. One that jumps by seconds means your device clock was corrected or drifted between checks.
Is a difference of a few seconds a problem?
For reading the time on this site, no. Its clocks use server time whatever your device says. For anything that depends on your device clock, turn automatic time on so the operating system corrects it.
Does this page set my clock?
No. A web page cannot change your device clock. It can only measure it and show the server time beside it. Changing the clock is your operating system's job, in its date and time settings.
Is the server an atomic clock?
No. The comparison is with this site's own server, which is enough to show a device that is seconds out. For time you can trace to a national standard, use a national time service such as NIST's.
Sources
We checked each fact on this page against these sources on 2 October 2026. Times, offsets and clock changes come from the time zone database.