World Clock

IANA tz database identifiers like Asia/Seoul or America/Los_Angeles. The browser's Intl.DateTimeFormat handles daylight-saving transitions automatically.

Several places (India +5:30, Newfoundland −3:30, Nepal +5:45) use offsets that aren't whole hours. The formatter shows them as UTC±H:MM.

It's the difference between each zone's offset and your local zone at the reference time. If you're in Seoul (+9) and you compare with Los Angeles (−8 in winter), the diff is −17h.

Yes — all calculations use the browser's built-in Intl APIs, no network required after first load.

The US and the EU do not switch on the same dates. The US springs forward on the second Sunday of March and falls back on the first Sunday of November; the EU switches on the last Sundays of March and October. For roughly three weeks in March and one in late October the gap is 4 hours, not the usual 5. Because the offsets are recomputed for whatever reference time you set, picking a date inside that window shows the real gap rather than today's.

From the browser's own copy of the IANA time zone database, via Intl.DateTimeFormat. Nothing is bundled with this page, so a device that has not had an OS or browser update in a while can be wrong for any country that changed its rules recently — several have moved or abolished DST on a few months' notice. For a date far in the future, or a zone whose rules were just amended, confirm against a second device before you book anything.