Why is the difference not the same all year?

Because the two places change their clocks on different dates, or one of them does not change at all. New York and London are 5 hours apart for most of the year, 4 hours apart for the three weeks in March after the United States springs forward but before Europe does, and 4 hours apart again for the week in late October after Europe falls back but before the United States does.

Which places never change the difference?

Any pair where neither observes daylight saving — India and Japan, for instance, are permanently 3 hours 30 minutes apart. Pairs inside the same regulatory bloc are also stable: every European Union zone changes at the same instant, so Lisbon and Athens stay exactly 2 hours apart all year.

How is the difference calculated?

By asking your browser for each zone offset at the same instant and subtracting. That means it is correct at the moment you look at it, including in the middle of a change-over, rather than reading a stored number that was true last month.

What does a negative difference mean?

It means the second place is behind the first. The page says "ahead" or "behind" in words for exactly that reason — minus signs on time differences are read backwards by roughly half of everyone.

Time difference between any two time zones

Time difference

Pick two places and this shows how far apart they are right now — plus the exact dates over the next year when that gap changes, which is the part most tools leave out.

From

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When this difference changes

A worked example: New York and London

The most-searched pair on the internet, and a good illustration of why “five hours” is a half-truth. These dates come from the IANA database at build time — they are fixed facts, not a live reading.

From 2026-03-08London is 4 hours ahead of New York
From 2026-03-29London is 5 hours ahead of New York
From 2026-10-25London is 4 hours ahead of New York
From 2026-11-01London is 5 hours ahead of New York
From 2027-03-14London is 4 hours ahead of New York
From 2027-03-28London is 5 hours ahead of New York

Example, not the current time. Live times appear once the page loads.

Common questions

Why is the difference not the same all year?: Because the two places change their clocks on different dates, or one of them does not change at all. New York and London are 5 hours apart for most of the year, 4 hours apart for the three weeks in March after the United States springs forward but before Europe does, and 4 hours apart again for the week in late October after Europe falls back but before the United States does.
Which places never change the difference?: Any pair where neither observes daylight saving — India and Japan, for instance, are permanently 3 hours 30 minutes apart. Pairs inside the same regulatory bloc are also stable: every European Union zone changes at the same instant, so Lisbon and Athens stay exactly 2 hours apart all year.
How is the difference calculated?: By asking your browser for each zone offset at the same instant and subtracting. That means it is correct at the moment you look at it, including in the middle of a change-over, rather than reading a stored number that was true last month.
What does a negative difference mean?: It means the second place is behind the first. The page says "ahead" or "behind" in words for exactly that reason — minus signs on time differences are read backwards by roughly half of everyone.

Time difference

When this difference changes

A worked example: New York and London

Common questions

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