Convert time across zones

A time zone is a region that keeps one common clock time. The Earth turns 15 degrees of longitude each hour, so the world divides roughly into 24 of them, each an hour apart from its neighbours.

Before that, every town set its clocks by its own solar noon. Railways made this unworkable — a timetable is useless if every station keeps different time — so standard zones were adopted through the 1880s.

Zones today are defined as offsets from UTC. In practice their boundaries follow national borders rather than lines of longitude, which is why the map is irregular.

It converts your time to UTC, then applies the target zone's offset for that date. The zone data comes from the IANA Time Zone Database via your browser, which is the same source your operating system uses.

• UTC first: your input is normalised to a single reference before anything else happens
• Then the destination offset: applied for the specific date, not a fixed number
• Daylight saving included: the offset used is whichever is actually in effect on that date in that place
• Updates as you type: no submit step, no page reload

Because the data comes from the browser's own database, it stays current with each browser release as countries change their rules.

A number of countries sit on half- or quarter-hour offsets, usually because a whole-hour zone would have put the clock noticeably out of step with daylight across their territory.

• India — UTC+5:30, a single zone for the whole country
• Nepal — UTC+5:45, the only 45-minute offset in the world
• Iran — UTC+3:30
• Afghanistan — UTC+4:30
• Myanmar — UTC+6:30
• Chatham Islands — UTC+12:45

These are worth knowing about because rounding to the nearest hour puts a meeting in the wrong place by thirty minutes.

Daylight saving shifts a region's clocks forward by an hour for part of the year. Around 70 countries observe it, and they don't switch on the same dates.

• Not universal: most of Asia and Africa don't observe it at all, and within the United States, Arizona and Hawaii opt out
• Different dates: North America switches in March and November, the EU at the end of March and October
• The gap moves: for a few weeks each spring and autumn, the difference between two cities is not the one you remember
• Southern hemisphere: switches in its own summer, so the difference to Europe changes by two hours across the year rather than one

The converter applies whichever offset is actually in effect on the date you enter, so those transition weeks are handled without you having to track them.

Near enough for scheduling — they're within 0.9 seconds of each other — but they're different kinds of thing.

• GMT is solar time measured at Greenwich, so it inherits the slight irregularity of the Earth's rotation
• UTC is atomic time, kept aligned with the Earth by occasional leap seconds
• Usage: UTC is the standard for computing, aviation and science; GMT today mostly names the UK's winter time zone

The practical catch is that the UK uses British Summer Time, UTC+1, from late March to late October — so "GMT" in a July invite usually means London time, which isn't what it says. Write UTC if you want to be unambiguous.

More detail in UTC vs GMT: What's the Difference?

Most unexpected results come down to one of these:

• The date. Near a daylight saving transition the difference between two places changes for a few weeks
• The city. Several place names exist in more than one country or state — check you picked the intended one
• The day. Across a large enough gap the result falls on a different date, which is easy to miss when the hour looks plausible
• Your device. If your own system clock or zone is set incorrectly, every conversion from local time inherits that error

If something still looks wrong after those, please get in touch — it's useful to know.

Conversions use the IANA Time Zone Database through the browser's built-in internationalisation support — the same data behind the clock on your phone and computer.

• Historical and future dates are converted using the rules that applied then, not today's
• Daylight saving is applied per date and per location
• Rule changes arrive with browser updates, since the database is maintained centrally and shipped with the browser

One practical limit worth stating: when a government announces a change at short notice, there's a lag before it reaches everyone's browser. That affects every tool built on this data, including this one.

Those are both good and have been around far longer. The difference is scope rather than correctness — they all read the same time zone database.

• TimeAndDate is far more comprehensive, covering calendars, astronomy, holidays and historical data. If you need breadth, use it
• Time.is is excellent at showing the current time precisely, with less emphasis on planning across several places
• TimeZonder is built around converting and comparing: the converter, a meeting planner, and world clocks, with no account and nothing held back

If you mostly need to answer "what time is it there, and when can we all meet", this is meant to do that quickly. For anything broader, the others are better tools.

That's what the meeting planner is for. It compares working hours across several locations and shows which slots are reasonable for everyone.

• Multiple participants: add as many locations as the meeting needs
• Working hours shown: each city is shaded by what time of day it is there, so unreasonable slots are visible at a glance
• Calendar export: send a chosen time to Google Calendar, Outlook, or download an .ics file for Apple Calendar
• Shareable results: copy a formatted result or a link that reopens the same comparison

For recurring meetings it's worth re-checking after each daylight saving changeover, since that's when a standing slot quietly moves for one side.

Yes. There's no account, no paywall and no limit on conversions — every tool on the site is available to everyone.

• Unlimited conversions between any supported zones
• All tools included: converter, world clocks, meeting planner and time difference
• No sign-up: nothing to create, nothing to verify
• Works on any device with a modern browser

Running costs are covered by advertising and by optional Ko-fi support from people who use it regularly. Ads only load after you've made a choice in the consent banner.

Largely, once you've loaded the site at least once. A service worker caches the page, its scripts and the city data, so conversions keep working without a connection.

Available offline:

• Converting between any city in the bundled list
• World clocks and the day strip
• Time difference and the meeting planner, if you opened those tabs while online

Needs a connection:

• Loading the site for the first time on a device
• Picking up time zone rule changes, which arrive with browser updates
• Calendar export, which hands off to an external service