How it is worked out
difference = offset of the destination − offset of the origin
Why it is done this way
Every zone has an offset from universal time, and that offset changes twice a year in countries that use daylight saving. So the difference between two cities is not a fixed number: between March and October it can be an hour more or an hour less than the rest of the year.
Step by step
- Look up the offset of the first city from UTC
- Look up the offset of the second
- Subtract the first from the second
- The result is how far ahead or behind the second city runs
What is worth knowing
The weeks when one country has already changed its clocks and the other has not are the ones that break meetings. The European Union changes on the last Sunday of March and of October; the United States on the second Sunday of March and the first of November; Mexico stopped changing in 2022 except along the border strip. During those two or three weeks the difference with America shifts by an hour, and this page works it out for today using the system's own zone database, which updates itself.