Time zone converter
A time zone converter shows one instant rendered in several places at once, in 12-hour or 24-hour form. Offsets are not fixed: most of Europe and North America shift by an hour twice a year on different dates, so London and New York are five hours apart for most of the year and four for two short stretches.
How to use it
The offsets and daylight-saving rules come from the browser’s own copy of the IANA time zone database rather than from a table stored here, which means they stay correct when a country changes its rules, and they do, several times a year. Zones that observe daylight saving are marked, because those are the ones where a meeting booked in March moves in October.
The clock switch matters more than it looks. On the 12-hour reading midnight is 12:00 am and noon is 12:00 pm, so the same number carries the two instants furthest apart in the day, which is why a meeting written as 12:00 is the one people miss by twelve hours. The 24-hour reading has no such hour, and that is why aviation, hospitals and most of the world outside North America schedule in it.
When you write the agreed time down, name the place rather than the abbreviation. "CET" is only true in Amsterdam and Paris for the winter half of the year — the summer half is CEST, an hour later — so a recurring invitation pinned to CET silently drifts every March. The abbreviations are ambiguous as well as seasonal: IST is Indian, Irish and Israel Standard Time; CST is Central Standard in the US, China Standard and Cuba Standard. "15:00 Amsterdam" or "15:00 Europe/Amsterdam" cannot be misread, and "14:00 UTC" is the one form that never moves.
What people use it for
- Finding a meeting hour that works across three offices
- Checking what time a call lands for someone abroad
- Seeing which of two places has already changed its clocks
- Writing a time into an invitation so it cannot be read two ways
- Checking a recurring meeting has not drifted after a clock change
Questions
Because daylight saving starts and ends on different dates in different places. For two weeks in March, London and New York are four hours apart rather than five.
That the zone observes daylight saving at some point in the year. Zones without it, most of Asia and Arizona among them, keep one offset all year.
Any zone your browser knows, which is the full IANA list of several hundred. Search by city name; the zone identifier is what gets added.
Near enough for scheduling. UTC is the atomic-clock standard and GMT is a time zone that happens to sit on it; they never differ by as much as a second.
The city. CET is only correct for the winter half of the year — the summer half is CEST — so a time written as CET moves by an hour every March. "15:00 Amsterdam" or a plain UTC time cannot drift.
Because several zones share them. IST is Indian, Irish and Israel Standard Time; CST is Central Standard in the US, China Standard and Cuba Standard. The IANA identifiers exist precisely to avoid this.
Yes. The clock switch flips every zone between 12-hour and 24-hour at once.
Your device’s. If that is wrong, every zone here is wrong by the same amount.