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World clock

Add cities to compare their current local times, dates and offsets at a glance.

How World clock works

World Clock displays the current local time for a set of cities or IANA timezones side by side, updating live from your device's clock. Each clock panel shows the city name, the current time, the date and the UTC offset currently in effect. It uses the browser's Intl.DateTimeFormat API with the relevant IANA timezone identifier, so DST transitions are handled automatically without any server query.

Because everything derives from your device clock and local Intl data, the world clock works offline once the page is loaded. You can add and remove cities from the display to build a personalised panel of the locations you care about most. The tool does not call any time-sync API; it trusts your device's system clock, which in most cases is synchronised via NTP and accurate to within a second.

Written by Bastien Sulyan

How to use World clock, step by step

  1. Browse the default city selection or search for a specific city name or IANA timezone.
  2. Add the cities you care about to your panel.
  3. Remove any city you do not need by clicking the remove button on its panel.
  4. Read each panel for the local time, the date and the UTC offset in effect there.
  5. Keep the tab open for a live side-by-side view as the seconds tick.

Common use cases

  • A remote team with members in Tokyo, London and Chicago keeps the world clock open in a browser tab for quick reference during video calls.
  • A trader monitoring international markets glances at the world clock to know which exchanges are currently open during overlap hours.
  • A travel blogger coordinating interview slots with sources in multiple continents uses the tool to instantly see what time it is for each contact.
  • A developer testing a globally distributed system checks local times across server regions to correlate log entries with business hours.

Frequently asked questions

How does the world clock get the current time?

It reads your device's system clock via the JavaScript Date API and then converts that single timestamp into each timezone's local time using Intl.DateTimeFormat. There is no call to an external time service. The accuracy of the displayed times depends on how accurately your device's clock is set.

Are the displayed times adjusted for daylight saving time?

Yes. Intl.DateTimeFormat uses the full IANA timezone database, which includes DST transition rules for every named timezone. The UTC offset displayed for each city reflects the current actual offset, not a nominal standard offset.

Can I rearrange the order of the city panels?

The order in which you add cities determines their position. To reorder, remove and re-add the cities in the sequence you prefer. A drag-to-reorder interface is not currently available.

Does the world clock update automatically, or do I need to refresh?

The display updates every second using a JavaScript interval tied to your local clock. There is no need to refresh the page. If you leave the tab open overnight, the times shown the next morning will still be correct.

Can I use this tool offline, for example on a flight?

Yes, once the page has loaded into your browser cache. The time calculations use only your device clock and locally stored Intl data. No internet connection is required after the initial page load.

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