Everyone who works across the Atlantic knows London is five hours ahead of New York. It is the kind of fact you stop checking. And for 337 days of 2026 it is right.
On the other 28 days it is four hours, and a meeting booked from memory happens an hour earlier than everyone expected.
Why the gap moves
Both countries put their clocks forward in spring. They just do not do it on the same day. America moves on the second Sunday in March. Britain waits until the last Sunday. That leaves three weeks when America has already sprung forward and Britain has not.
The same thing happens in reverse in autumn, and the window is shorter. Britain goes back on the last Sunday in October, America on the first Sunday in November.
| 2026 | What happens | London to New York |
|---|---|---|
| 8 March | America springs forward | 4 hours |
| 29 March | Britain springs forward | 5 hours |
| 25 October | Britain falls back | 4 hours |
| 1 November | America falls back | 5 hours |
Twenty-one days in March and seven in October. Twenty-eight in total, every year, and the dates move around because they are tied to which Sunday it is rather than to a date.
There is no such thing as the difference between two cities. There is only the difference today.
It is worse from India
India does not change its clocks at all. That sounds simpler, and for India alone it is. But it means every country that does change is a moving target from here.
New Delhi to London is four and a half hours for part of the year and five and a half for the rest. Not for a three-week window — for 155 days of 2026. New Delhi to New York shifts on 127 days.
Sydney is the one that has no normal answer at all. Australia's daylight saving runs through the southern summer, which is our winter, so the gap flips halfway through the year and stays flipped.
| New Delhi to | Most of the year | The rest |
|---|---|---|
| London | 4½ hours behind (210 days) | 5½ hours behind (155 days) |
| New York | 9½ hours behind (238 days) | 10½ hours behind (127 days) |
| Sydney | 5½ hours ahead (183 days) | 4½ hours ahead (182 days) |
Delhi to Sydney is five and a half hours for 183 days and four and a half for 182. There is no usual figure to remember. It changes on 5 April and again on 4 October, and half the year is on each side.
What to do instead of remembering
Do not store the difference. Store the cities, and work the difference out each time from the date you actually mean.
That is not extra effort if something else does it. Every computer and phone already carries the full rulebook — the IANA time-zone database, updated whenever a government changes its mind. Any tool that reads from it gets the awkward weeks right without being told about them. Any tool that stores a number per pair of cities is wrong for 28 days a year and will not tell you which 28.
The quick test for a converter: ask it for 09:00 New York on 10 March 2026 and again on 10 April. If both answers are the same time in London, it is using a stored number and you should not trust it in March.