Sources and accuracy
Every offset and clock-change date on this site comes from one place: the IANA time zone database.
The IANA tz database
The IANA Time Zone Database (also called tzdb, tzdata or the Olson database) records the history and current rules of civil time for every region, keyed by names like Europe/Paris. It is maintained by volunteers, coordinated by IANA and described in RFC 6557. Operating systems, browsers and programming languages all ship a copy.
How this site uses it
- Live tools (converter, clocks, "what time zone am I in") run in your browser using the JavaScript
IntlAPI, which reads your browser’s bundled copy of tzdb. Nothing is typed in by hand. - Reference pages (daylight saving dates, offset list, zone-to-zone tables) were generated by a script from tzdb release 2026c, as bundled with Node.js’s ICU library, when the site was built.
- Country names for zones come from the
countries-and-timezonespackage, which is derived from tzdb’szone1970.tab. Abbreviations come from Unicode CLDR, supplemented with a few widely used ones CLDR omits.
Limits
Rules change by government decision. Countries adjust or abolish daylight saving time, sometimes with only weeks of notice (Egypt reinstated DST in 2023; Mexico abolished most of it in 2022). tzdb is updated when that happens, but your browser only learns about it after an update, and reference pages only after a rebuild. For anything critical far in the future, check with an official source for that country.
Your device clock. Live clocks read your device’s time. If it is wrong, every clock here is wrong by the same amount.
Abbreviations are ambiguous. CST, IST and BST each mean several things. Pages state which zone they use.