How to use
- The check runs as soon as the page opens and shows within seconds how fast or slow your clock is, and how precise the measurement is.
- The large clock shows the corrected time; switch between your time zone, UTC and other zones.
- To wait for an exact moment, enter the target time under Countdown and tick the box for beeps in the last 3 seconds.
- If your clock is noticeably off, turn on automatic time setting as described below.
Options explained
- Fast or slow
- Your device clock minus the exact time; positive means fast, negative means slow. Within 0.1 seconds counts as spot on.
- Precision
- Eight round trips are measured and the fastest is used; the error is at most half of that round trip, usually a few to a few dozen milliseconds.
- Reference
- Our server’s clock, which is kept in sync with time servers over NTP to within a millisecond.
How to keep your clock accurate automatically
| Device | Setting |
|---|---|
| Windows 10 / 11 | Settings → Time & language → Date & time: turn on “Set time automatically”, then click “Sync now” |
| macOS | System Settings → General → Date & Time: turn on “Set time and date automatically” |
| iPhone / iPad | Settings → General → Date & Time: turn on “Set Automatically” |
| Android | Settings → System → Date & time: turn on automatic date and time (menu names vary by brand) |
On Windows, the default time server is time.windows.com. If syncing fails, you can switch to pool.ntp.org or time.google.com under Control Panel → Date and Time → Internet Time → Change settings.
How a web page measures the offset
Browsers cannot use the NTP protocol, so the page does the same thing over HTTP: it notes your clock when the request leaves, the server replies with its time, and the round trip is timed. Assuming the trip out and back take equally long, the server’s reading corresponds to “send time + half the round trip” on your clock; the difference is your offset. Uneven trips cause error, but never more than half the round trip, which is why the fastest of eight trips is used.
To see the time around the world, use the world clock; for simple timing, try the online timer.
Frequently asked questions
Is this an atomic clock?
Not directly. Our server synchronises with NTP time servers, which are themselves traced back to atomic clocks, so the time shown here is within a few milliseconds of official time plus the measured network error.
Which clock counts in a flash sale?
The shop’s server clock. Those servers are normally synced to official time too, so the corrected time here tells you how long is left — but your click still has to travel over the network, which adds tens to hundreds of milliseconds on a slow connection.
My clock is a few seconds slow. Does it matter?
Rarely in daily use. It matters for sales, ticket releases, clocking in and timed exams. A clock that is off by many minutes can also break logins and HTTPS certificate checks.
Why do my phone and computer give different results?
Each device keeps and syncs its own clock. Phones usually take the time from the mobile network or a time server and are often more accurate than computers.
Privacy
This tool runs in your browser. It only fetches public data (such as the exact time or orbital data) or passes pairing details through our server; your files, text and location are not uploaded. Server access logs record IP addresses and request URLs, used only to prevent abuse.