How does the world clock know each timezone's time?

It uses your device clock as the single source of truth, then formats that exact instant into each timezone with the browser's built-in Intl.DateTimeFormat API. Daylight saving transitions are handled automatically by the IANA timezone database.

What is an IANA timezone name?

IANA timezone names look like Region/City — for example Europe/London or America/Los_Angeles. They encode the full history of UTC offsets and daylight saving rules for that location, which is why they are more reliable than fixed offsets like GMT+1.

Does it handle daylight saving time?

Yes. Because it relies on the IANA database baked into your browser, each clock automatically shifts when a region enters or leaves daylight saving time, so the displayed offset is always current.

Is my location or data sent anywhere?

No. The clock reads only your local device time and runs entirely in your browser. Nothing is uploaded and no network request is made.

Why does a city show a different offset than I expected?

Offsets change across the year due to daylight saving, and some regions have unusual rules. The tool always reflects the live offset for the current instant, so a summer reading may differ from a winter one.

Multi-Timezone World Clock

A multi-timezone world clock lets you watch the current time in several places at once — handy for scheduling calls across continents, coordinating remote teams, or tracking markets. This free tool pins any number of IANA timezones to a board and updates each one live, every second, directly in your browser.

How it works

There is only one real moment in time. The tool captures the current instant from your device clock and then renders that same instant into each chosen timezone using the browser’s Intl.DateTimeFormat API with the timeZone option set to an IANA name such as Asia/Tokyo.

Because formatting is delegated to the IANA timezone database, daylight saving transitions and historical offset changes are handled automatically. The UTC offset shown next to each clock is derived from the same formatter, so it always matches the live rule for that region.

Tips and notes

Use full IANA names (Region/City) rather than fixed offsets — they survive daylight saving changes.
Add UTC to keep a stable reference point alongside local zones.
The seconds tick from your own device, so if your computer clock is wrong, every zone will be equally wrong by the same amount.

Everything runs locally — no clock data is ever sent to a server.