Time Zone Converter

One moment, everywhere at once

Set a date, a time and the zone you are thinking in. Then add a row for every place that needs to be in the room. Each shows its local time, the offset actually in force on that date, and a marker when the day is different there.

The whole list lives in the page address, so a link you send opens with everyone’s zone already in it.

Everything runs in your browser, using its own copy of the time zone database.

Why it asks for a date

Because a time zone is not an offset. This is the single idea that makes time zone code correct or wrong, and most tools skip it.

New York is UTC−5 in January and UTC−4 in July. London is UTC+0 and UTC+1. Sydney is the other way round, because its summer is our winter. A converter that stores “New York = −5” is right for about four months a year.

Worse, the two ends rarely change on the same weekend. The United States springs forward in early March and Europe in late March, so for three weeks each spring London is four hours ahead of New York rather than five. A standing call in that window quietly moves by an hour, which is exactly the kind of thing nobody notices until the third missed meeting.

So the converter takes a date, looks up what the offset really was on that day, and shows it beside the answer.

The day can be different

The inhabited world spans 25 hours, from UTC−11 in Midway to UTC+14 in Kiritimati. That is more than a day, which has two consequences people underestimate.

First, a shifted date is routine rather than exotic. 10pm Wednesday in New York is already Thursday in London, Tokyo and Sydney. Any call scheduled after about 6pm on the American east coast is on tomorrow’s calendar for most of Asia.

Second — and this genuinely surprises people — two places can be on dates two days apart. When it is 11pm on the 16th in Midway, it is midnight on the 18th in Kiritimati. It lasts only an hour a day, but it is why the day shift here is a number rather than a “next day” badge.

The tool prints the shift on every row. Left to be noticed, it gets noticed late.

Times that do not exist

When the clocks go forward, an hour is deleted. On 8 March 2026 in the United States, 01:59:59 is followed by 03:00:00 — and 02:30 never happens at all.

Ask most converters for 02:30 that day and they will hand back some instant without comment, usually the wrong one. This tool detects it, moves the time forward past the gap, and says so:

“02:30 does not exist on this date in that zone — the clocks jump forward over it. Shown as 03:30 instead.”

Shifting forward is what calendar software does with a meeting scheduled into the missing hour, so it is the least surprising behavior. The important part is being told, because a recurring meeting at 02:30 is a real thing people set up and it does something odd once a year.

Times that happen twice

The reverse case, in autumn. Clocks go back, an hour repeats, and 01:30 occurs twice — an hour apart, with two different offsets.

There is no correct answer here, only a choice. This converter uses the first occurrence, which is the earlier instant and the convention most systems follow.

The practical advice: anything scheduled inside a repeated hour is genuinely ambiguous, and no tool can resolve it for you. If it matters — a shift handover, a market open, a backup window — confirm it as UTC rather than as a local time.

Why UTC exists

UTC is the reference every zone is defined against. It does not observe daylight saving and it never changes, which is what makes it useful.

The rule of thumb worth keeping: store and communicate in UTC, display in local time. A log line, a database column, a calendar invite’s underlying value and an API response should all be an unambiguous instant. Local time is a presentation format — it is what you render at the last possible moment, for one particular reader.

Systems that store local time break in three predictable ways: twice a year around the transitions, whenever a government changes a rule, and permanently as soon as two users are in different places.

GMT is not quite the same thing as UTC, though for scheduling you can treat them as identical. GMT is a time zone; UTC is a time standard, defined by atomic clocks and nudged by leap seconds to stay near the Earth’s rotation.

Why some zones have no abbreviation

You will see EST and EDT for New York, and GMT+9 for Tokyo. That is not an omission — most of the world’s zones simply have no short name.

Abbreviations are largely a North American and European habit, they are not standardized, and several are actively ambiguous. CST means Central Standard Time in the United States, China Standard Time, and Cuba Standard Time, which are three different offsets. IST covers India, Ireland and Israel.

Where a real abbreviation exists, it is shown. Where one does not, an offset is shown instead, because an offset is never ambiguous and an invented abbreviation would be.

Where the rules come from

Your browser’s own copy of the IANA time zone database — the same dataset used by essentially every operating system, updated several times a year as governments change their rules.

Nothing about offsets is stored in this page. That is a deliberate constraint rather than a shortcut: a hardcoded table would be wrong within months of the next rule change, and it would be wrong silently. The tool would keep answering with total confidence, just incorrectly.

Because the browser holds the real database, this also works backwards. Ask for a date in 2010 and Moscow shows UTC+4, because Russia had not yet abolished daylight saving or moved to UTC+3. A table built today would get that wrong; the database does not.

Zones are named by region and city — Europe/London, Asia/Kolkata — rather than by country, because borders and rules change and city names mostly do not.

Offsets that are not whole hours

A last thing that catches out anyone doing this arithmetic by hand. Not every zone is an integer number of hours from UTC.

India is UTC+5:30. Nepal is UTC+5:45. The Chatham Islands are UTC+12:45. Parts of Australia run on half-hour offsets, and Lord Howe Island shifts by only thirty minutes when its daylight saving starts.

Mental arithmetic in whole hours will be half an hour out for about a fifth of the world’s population, most of them in India. The converter handles all of it, because the database does.

Frequently asked questions

Why does the converter ask for a date?

Because a zone is not a fixed offset. New York is UTC−5 in January and UTC−4 in July, and the two ends of a call rarely change their clocks on the same weekend. Without a date the answer is a guess; with one it is exact.

How do I plan a meeting across several zones?

Set the date, time and your own zone at the top, then add a row for each place you need. Every row shows the local time, the offset in force that day, and a marker when the date is different there. The page address carries the whole list, so the link you send opens with everyone's zone already in it.

Why does it say +1 day?

Because it is. The world spans 25 hours from UTC−11 to UTC+14, so 3pm Tuesday in London is Wednesday morning in Sydney — and at the extremes two places can be on calendar dates two days apart. The shift is printed rather than left to be noticed, because noticing it late is how meetings get missed.

What happens to a time that does not exist?

The tool says so. When clocks jump forward, an hour is skipped — 02:30 simply never happens that day. Rather than inventing a moment, it moves the time forward past the gap, which is what a calendar does with a meeting scheduled into the missing hour, and shows a warning explaining what it did.

What about a time that happens twice?

When clocks go back, an hour repeats. The converter uses the first of the two, which is the earlier instant and the convention nearly everything else follows. Anything scheduled in that hour is genuinely ambiguous and worth confirming in writing.

Where do the time zone rules come from?

Your own browser's copy of the IANA time zone database, which it updates along with itself. Nothing is hardcoded here — a table of offsets shipped in a tool would be wrong within months of some government changing a rule, and wrong without any sign of it.

Why do some zones show an offset instead of a name like EST?

Because most of the world's zones have no short name. Abbreviations are largely a North American and European habit, and several of them are ambiguous anyway — CST means three different things. An offset is unambiguous, so it is shown where no real abbreviation exists.