Online Tool Store
World Clock
See the current time in any set of cities side by side, each with its date and UTC offset, updating every second. Runs entirely in your browser.
🔒 This tool runs entirely in your browser. Your files are never uploaded to a server.
How it works
- Four clocks are shown to start with. Type a city or zone and press "Add clock" to add your own.
- Each card shows the local time, the date there, and the current UTC offset, refreshing every second.
- Switch to 24-hour time or hide seconds with the toggles; remove a city with ✕.
- Your list is remembered on this device, so the same clocks are waiting next time you open the page.
How the conversion is done
There is only ever one instant in time. Your device tracks it as a count of milliseconds since 1 January 1970 UTC, and a city's wall clock is that instant plus the region's offset:
local time = UTC instant + zone offset (at that instant)
The offset in brackets is the important part. It isn't a constant — Europe/London is UTC+0 in winter and UTC+1 in summer, and some regions have changed their rules outright. That's why each city is stored as an IANA zone name instead of a number: the browser looks up which offset applied at that exact moment, so the answer stays right across daylight saving changes and historical shifts.
It also explains the date line on each card. When London shows Tuesday morning, Tokyo is already nine hours ahead and can be on Tuesday evening, while New York is five hours behind and still on Monday night — same instant, three different calendar days.
FAQ
Where do the times come from?
Your own device. The clock reads your computer's current time and converts it into each zone using the time zone database built into your browser — nothing is fetched from a server, so no request is made and no list of the cities you watch is sent anywhere.
Does it handle daylight saving time?
Yes. Each city is stored as an IANA zone such as Europe/London rather than a fixed offset, so the displayed time and the UTC offset follow that region's daylight saving rules automatically, including on the changeover days.
Are my cities saved for next time?
Yes, in your browser's local storage on this device only — never on a server. Clearing site data or using private browsing resets the list to the defaults, and "Reset to defaults" does the same on demand.
What can I type in the search box?
Either a city name such as Paris or Colombo, or a full zone name such as Asia/Dubai. The dropdown lists every zone your browser knows, which is usually the complete IANA set of around 400 entries.
Why is my city missing?
The IANA database names one zone per region rather than per city, so smaller places share a nearby entry — Manchester is covered by Europe/London, and Bengaluru by Asia/Kolkata. Pick the zone your city belongs to and the time will be correct.
Is the clock accurate to the second?
It's exactly as accurate as your device's own clock, which it re-reads every second. If your computer's time is off, every clock here is off by the same amount — most systems fix this themselves by syncing with a network time server.
How we compare
| Feature | Online Tool Store | Ad-supported world clock sites | Your phone's clock app |
|---|---|---|---|
| No ads or pop-ups on the page | ✓ | ✗ | ✓ |
| No request made for the time — it's all local | ✓ | Varies — many track which cities you view | ✓ |
| Every IANA zone available, ~400 entries | ✓ | ✓ | Usually a shorter curated city list |
| Visible on a desktop screen while you work | ✓ | ✓ | ✗ |
| City list syncs across your devices | ✗ | Some do, with an account | ✓ |
| Meeting planner across several zones | ✗ | ✓ | ✗ |
This is for the everyday question — is it a reasonable hour to call the Colombo office, has New York started work yet — kept on a tab you can glance at, with no ads in the way and no record of who you're checking on. For picking a meeting slot that suits five zones at once, a dedicated planner still does more.