Time Zone Overlap Calculator

Add each person's city and the hours they work. This shows the window where everyone is inside their own working day — on a specific date, so it stays correct through every daylight-saving change.

City-pair overlap pages

Precomputed overlap windows for 351 pairs of cities. Each page shows both working days in local time and UTC, the hours they share, and how that window shifts through the year — whether the two cities change clocks on the same day, on different days, or not at all.

• New York and London
• New York and Bangalore
• London and Bangalore
• San Francisco and London
• New York and Tokyo
• New York and Sydney
• New York and São Paulo
• London and Sydney
• Chicago and Bangalore
• San Francisco and Bangalore
• New York and Paris
• Sydney and Auckland

How the overlap is calculated

Each person's working hours are converted into a single interval of absolute time, and the answer is the intersection of those intervals. Local clock times are worked out at the end, for display, from the instant — never by subtracting one clock from another.

That distinction is the whole point of taking a date. Twice a year the United States and Europe change clocks on different weekends, and most of the world never changes at all, so a tool that reasons in local time is wrong for exactly the meetings it was built to help with.

Questions

What is a time zone overlap calculator?

It answers a question a time zone converter cannot: not "what time is it there", but "which hours of the day are all of us at work". You add each person's city and their working hours, and it returns the window — if any — where every one of those hours coincides.

How do I find overlapping working hours across time zones?

Add one row per person with their city and the hours they are contracted to work, then read the overlap at the top. Add as many people as you like; the window is the intersection of all of them, so it shrinks as you add cities. If it comes back empty, nothing is broken — it means there is no hour on that date when everyone is inside their own working day.

Why does the overlap change twice a year?

Because countries change their clocks on different dates. In most years the United States and the European Union are out of step for roughly two weeks in March and one week in October or November, and the southern hemisphere changes in the opposite direction. A converter that subtracts one local time from another is wrong during exactly those weeks. This tool works in absolute time, so it stays right.

How do I schedule meetings across time zones without frustrating people?

Pick the window where everyone is inside their working hours rather than the window that is most convenient for the majority, rotate the unpopular slot between regions so the same people are not always the ones on a 07:00 call, and keep recurring meetings inside the overlap so they survive a daylight-saving change without moving.

Read the rest of the questions