Time Zone Difference Calculator

In short The difference between two time zones is not a fixed number, and treating it as one is the single most common scheduling bug. A UTC offset belongs to an instant, not to a place: each zone follows its own daylight saving rules, on its own dates, and roughly seven zones in ten follow none at all. So when only one side of a pair changes its clocks, the gap between them shifts by an hour — and because the two hemispheres and the two continents do not switch on the same dates, there are usually a few weeks each year when the gap is something it is not for the rest of the year. London and New York are five hours apart for 337 days of the year and four hours apart for 28 — three weeks in March, because America changes its clocks first, and one week at the end of October, because Europe changes back first. This page samples every day of the year and lists every value the difference actually takes, along with the dates it changes. If it reports more than one value, then any calendar entry, cron schedule or "we are always N hours apart" assumption built on a single number is wrong for part of the year — and it will be wrong precisely during the weeks people are trying hardest to get the timing right.