How is the time difference calculated?

The tool takes the moment you enter, treats it as wall-clock time in the source zone, and reformats it in the target zone using Intl.DateTimeFormat. It then subtracts the two zones' UTC offsets at that moment and shows the result, for example "Europe/London is 5 hours ahead of America/New_York".

Does the difference change across the year?

Yes. When one zone observes daylight saving time and the other does not, the offset shifts by an hour around the spring and autumn transitions. Pick the actual date you care about to get the correct difference.

Can I calculate the difference between two cities?

Yes. Type the IANA name closest to each city (for example America/New_York or Asia/Tokyo) into the source and target fields. The dropdown filters as you type.

Why is the difference sometimes 30 minutes or 45 minutes?

Several zones use offsets that are not whole hours, including India (UTC+5:30), Nepal (UTC+5:45), and parts of Australia. The IANA database handles these offsets automatically.

Time Difference Calculator

Find the time difference between two zones by picking a source, a target, and a reference moment. The tool shows the converted target time and the source time side by side, and states how many hours the target zone is ahead of or behind the source zone.

From timezoneTo timezone

Date and time (wall clock in source zone)

In Europe/London

Pick a date and time

Source: UTC

Pick a date and time

Quick target zones

How it works

The reference moment is anchored in the source zone, then Intl.DateTimeFormat re-renders the same UTC instant in the target zone using its IANA rules. The tool subtracts the two zones' UTC offsets at that instant and states the difference, which shifts automatically when one of the zones is in daylight saving time on the date you picked. Picking the actual day of an event reveals whether the usual offset will hold or change for that particular date.

Processing runs in your browser

All timezone math happens locally in your browser tab. Our servers are not involved at any point. You can see this yourself in your browser's DevTools Network tab.

Frequently asked questions

How is the time difference calculated?: The tool takes the moment you enter, treats it as wall-clock time in the source zone, and reformats it in the target zone using Intl.DateTimeFormat. It then subtracts the two zones' UTC offsets at that moment and shows the result, for example "Europe/London is 5 hours ahead of America/New_York".
Does the difference change across the year?: Yes. When one zone observes daylight saving time and the other does not, the offset shifts by an hour around the spring and autumn transitions. Pick the actual date you care about to get the correct difference.
Can I calculate the difference between two cities?: Yes. Type the IANA name closest to each city (for example America/New_York or Asia/Tokyo) into the source and target fields. The dropdown filters as you type.
Why is the difference sometimes 30 minutes or 45 minutes?: Several zones use offsets that are not whole hours, including India (UTC+5:30), Nepal (UTC+5:45), and parts of Australia. The IANA database handles these offsets automatically.

Last reviewed September 30, 2026

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