Time zone converter
A time in one zone, shown in another — and when each of them next changes its clocks, because an offset is not a time zone. Nothing you type here leaves your browser — it is worked out on your own device, so there is nothing to send and nothing to log.
An offset is not a time zone
“UTC+1” is a number. “Europe/London” is a rule that produces different numbers on different dates. London is UTC+0 in January and UTC+1 in July, and a meeting stored as “UTC+1” is simply wrong for five months of the year.
Worse, the rules change. The IANA time zone database — which is what your browser, your phone and this page all use — is updated several times a year, because governments keep moving their clocks. Egypt abolished daylight saving and then brought it back in 2023. Brazil abolished it in 2019. Store a zone and your calendar follows; store an offset and it goes wrong without anything having failed.
Everybody changes on a different weekend
The United States springs forward on the second Sunday in March; Europe on the last Sunday in March. So for about three weeks every spring, New York is four hours behind London instead of five, and every recurring transatlantic meeting in the world moves by an hour for one of the two ends. The same happens in autumn, in reverse, for one week.
The tool above finds the changes by walking the year and watching the offset, which is the only honest way — there is no list of transitions that stays true, which is precisely the point.
Not every offset is a whole hour
| India | UTC+05:30, and the whole country on one zone despite being nearly 3,000 km wide. |
|---|---|
| Nepal | UTC+05:45. Forty-five minutes, deliberately chosen to be distinct from India's. |
| Chatham Islands | UTC+12:45, and daylight saving on top of it, so it is UTC+13:45 in the southern summer. |
| Lord Howe Island | UTC+10:30, and its daylight saving shift is thirty minutes, not sixty. It is the only place that does this. |
Any code that stores offsets as whole hours is wrong for about a fifth of the world's population.
What it will not do
- It will not use a zone list of its own. The list, the rules and the transitions all come from your browser's copy of the IANA database, which updates when your browser does. A table baked into this page would be stale within months.
- It will not know about a change a government announces tomorrow. Nothing can until the database is updated and shipped — historically that has sometimes been a matter of weeks' notice.
- It will not handle the hour that happens twice. When the clocks go back, one local hour occurs twice, and “01:30” that night is genuinely ambiguous. This page takes the first.