Why does my country not show up?

The picker lists common zones to keep the UI compact. Any IANA identifier the browser supports will work — open an issue if you need one added to the dropdown.

Why are transitions always at strange-looking times?

Most zones change at 02:00 or 03:00 local time, so on the spring-forward day, the wall clock jumps directly from 01:59 to 03:00 (for example). The tool shows the minute before and after the jump so you can see the boundary clearly.

Does this account for historical rule changes?

Yes — the calculation runs against the tzdb your browser ships, which includes the historical rules. If your OS is very old, very recent rule changes may be missing.

Some zones observe a 30-minute DST shift. Will the tool show that?

Yes. The reported shift is in minutes, so 30-minute shifts (e.g. Lord Howe Island) show up as +30 / -30 instead of ±60.

Daylight Saving Time Calculator

Find DST start and end transitions for any IANA time zone and year.

Written by Golam Rabbani, Founder & Lead Engineer

This interactive tool requires JavaScript. Read the formula and worked example below; you can compute the result by hand.

How to use this daylight saving time calculator

Pick the IANA time zone you want to check.
Enter a year between 1970 and 2099.
Press "Find DST transitions".
Read the spring-forward and fall-back wall-clock times, plus the standard and daylight offsets.
Use Reset for a new lookup or Copy to share the result.

About this daylight saving time calculator

Daylight Saving Time (DST) shifts the local wall-clock by one hour (sometimes 30 minutes) for part of the year so evenings get more daylight. This tool finds the exact minute on which DST starts and ends in any IANA time zone using your browser’s built-in tzdb (the same one the operating system uses).

It works by sampling the zone’s UTC offset in January and in July. If the offsets match, the zone does not observe DST that year. If they differ, the tool runs two binary searches — one in the first half of the year, one in the second — narrowing each transition to the minute. The result includes the local times immediately before and after the change, the shift in minutes, and both the standard and daylight offsets formatted as <code>UTC±HH:MM</code>.

Worked example: select Europe/London for 2026. The tool reports a spring-forward on 29 March 2026 at 01:00 → 02:00 (+60 min) and a fall-back on 25 October 2026 at 02:00 → 01:00 (-60 min), with standard offset UTC+00:00 and daylight offset UTC+01:00. Useful for setting up cron jobs, scheduling meetings around the gap, or remembering when to change your clocks.

The dates and offsets are sourced from the browser, so they reflect the most recent tzdb update shipped with your OS or Node runtime.

FAQ

Why does my country not show up?: The picker lists common zones to keep the UI compact. Any IANA identifier the browser supports will work — open an issue if you need one added to the dropdown.
Why are transitions always at strange-looking times?: Most zones change at 02:00 or 03:00 local time, so on the spring-forward day, the wall clock jumps directly from 01:59 to 03:00 (for example). The tool shows the minute before and after the jump so you can see the boundary clearly.
Does this account for historical rule changes?: Yes — the calculation runs against the tzdb your browser ships, which includes the historical rules. If your OS is very old, very recent rule changes may be missing.
Some zones observe a 30-minute DST shift. Will the tool show that?: Yes. The reported shift is in minutes, so 30-minute shifts (e.g. Lord Howe Island) show up as +30 / -30 instead of ±60.