Time Difference Calculator

This is not a world clock, and it is not a time-zone converter

Three tools get confused with each other, and picking the wrong one is why people end up doing the arithmetic twice.

• A world clock shows what time it is in a list of places right now. It answers "is it rude to call?"
• A time-zone converter takes one moment and shows it in many places at once. It answers "I want to hold this meeting at 15:00 my time — what is that for everyone invited?" Use that one when you are scheduling across a team.
• This page compares exactly two places and tells you the size of the gap between them, whether daylight saving is bending it, and when it is about to change. It answers "how far apart are we, and is that about to stop being true?"

The gap is the thing worth knowing because it is the thing you remember. Once you know London and New York are five hours apart you can do every future conversion in your head — until one of them changes its clocks and the other has not yet, which is the whole reason this page exists.

The two weeks a year when everything is wrong

The United States moves its clocks forward on the second Sunday in March. Europe moves on the last Sunday in March. For those two or three weeks the gap between New York and London is four hours, not the five everybody has memorised, and a recurring meeting that was fine all winter lands an hour out. The same happens again in autumn, when the US falls back a week after Europe does.

The southern hemisphere makes it worse, because its clocks move the opposite way at the opposite time of year. Between London and Sydney the gap swings between 9, 10 and 11 hours depending on the month, and there is no single number you can memorise. A calendar invite handles this correctly if it stores a zone; a note in a document that says "3pm your time, 11pm mine" does not.

Why offsets are never hardcoded here

Time zones are political, not astronomical, and they change with very little notice. Egypt reintroduced summer time in 2023 after seven years without it. Mexico abolished most of its daylight saving in 2022. Kazakhstan merged its two zones into one in 2024. Lebanon moved a clock change by decree with 48 hours of warning in 2023, and phones across the country disagreed with each other for days.

The only defence is to never store an offset. This page reads every offset from your own browser's copy of the IANA time-zone database, by formatting an actual instant in the zone and measuring the difference, which is why the answer follows whatever the current rules are rather than whatever was true when the page was written. If your device is up to date, this page is up to date. If a rule changed yesterday and your operating system has not caught up, no website can save you — and that, rather than the arithmetic, is the real hazard in this whole subject.

The half-hour and quarter-hour zones people forget

Not every offset is a whole number of hours. India is UTC+5:30 and has been on one zone since 1947 despite spanning nearly thirty degrees of longitude. Iran is +3:30, Afghanistan +4:30, Myanmar +6:30, and the Australian state of South Australia is +9:30 or +10:30 depending on the season. Nepal is +5:45 — fifteen minutes ahead of India, which is a deliberate assertion of independence rather than an accident of geography. The Chatham Islands run +12:45. Any tool that only offers whole hours is quietly wrong for about a fifth of the world's population, which is why this one reports minutes.

The practical rules

• Name the zone, not the offset. "09:00 New York time" survives a clock change. "09:00 EST" does not, because half the year New York is not on EST at all, and "14:00 UTC" quietly moves for one side of the call.
• Check the gap for the actual date of the meeting, not for today. That is what the date box above is for, and it is the single most common cause of a missed call across the Atlantic in late March.
• Beware abbreviations that collide. CST is Central Standard Time in the US, China Standard Time and Cuba Standard Time. IST is India, Ireland and Israel. Write the city.