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.

What is the Multi-Timezone World Clock?

Free multi-timezone world clock — view the live current time across any IANA timezones (London, New York, Tokyo, and more) side by side, updating every second in your browser. It runs free in your browser on Gera Tools, with nothing uploaded.

Multi-Timezone World Clock

Name: Multi-Timezone World Clock
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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.

Why a world clock is more useful than UTC arithmetic

The straightforward way to work across timezones is to know the UTC offset for each location and add or subtract manually. In practice this fails because offsets are not fixed year-round: most countries in the Northern Hemisphere advance their clocks in spring and retract them in autumn (daylight saving time), and the exact dates of those transitions vary by country. The United States and Europe, for example, switch on different dates in March and November, which means that for a few weeks each year the offset between New York and London is one hour different from what it is the rest of the year.

Pinning live IANA timezone clocks to a board eliminates this arithmetic entirely. The clock always shows the right local time, automatically accounting for whether each location is currently on standard or daylight saving time.

Practical uses for remote teams

The most common use case is scheduling recurring meetings with team members in different regions. When you pin all the team’s timezones to the board and look at them simultaneously, the right meeting window is immediately visible: you can see which hours overlap with everyone’s working day without constructing a time zone conversion table.

A secondary use case is tracking financial market opening and closing times. Major exchanges — New York Stock Exchange, London Stock Exchange, Tokyo Stock Exchange, Hong Kong Stock Exchange, Frankfurt — each have opening and closing times in their local timezone, and seeing them all on one board makes it easy to know when each market is live without memorising the offset from your own timezone.

Key timezones for common use cases

North American business: America/New_York (Eastern), America/Chicago (Central), America/Denver (Mountain), America/Los_Angeles (Pacific), America/Toronto (same as Eastern), America/Vancouver (same as Pacific)

European business: Europe/London (UK and Ireland), Europe/Paris / Europe/Berlin / Europe/Amsterdam / Europe/Rome (CET/CEST, identical offset), Europe/Stockholm, Europe/Zurich

Asia-Pacific business: Asia/Tokyo (JST, UTC+9, no daylight saving), Asia/Shanghai (CST, UTC+8, no daylight saving), Asia/Hong_Kong (HKT, UTC+8), Asia/Singapore (SGT, UTC+8), Asia/Mumbai (IST, UTC+5:30), Australia/Sydney

Adding UTC as a stable reference point makes it easy to convert any local time to an absolute reference without depending on the offset displayed by any specific zone.

Tips and notes

Use full IANA names (Region/City) rather than fixed offsets — they survive daylight saving changes without any adjustment.
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. Keep your device clock synchronised to an NTP server for accurate results.
Pins persist within your browser session. Refresh the page to start with a clean board.

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