List of time zones

The table isn't typed in by hand. When the page opens, it asks your browser for every time zone it knows,^[1] then works out each one's offset, abbreviation and next clock change from the IANA time zone database built into the browser.^[2] That's why it's right whatever the season, and why it updates when a country changes its rules and your browser gets the new data.

It depends what you count:

• Offsets: nearly 40 are in use, from UTC−12 to UTC+14, including half-hour and 45-minute ones.^[3] The headings in the table are these.
• Zone IDs: a few hundred. Each ID stands for a region whose clocks have agreed since 1970, so places on the same offset today can still have different IDs because their history or their daylight saving rules differ.^[4]

To see where each zone lies, look at the time zone map.

IDs follow the pattern Area/Location: a continent or ocean, then a city that represents the zone, like Europe/Paris or America/Argentina/Buenos_Aires.^[4] The city is a representative, not a capital: Germany is Europe/Berlin, but much of the US Midwest is America/Chicago. More in the guide to the IANA time zone database.

Abbreviations are handy but not unique. CST means one thing in North America and another in China, and IST can mean India, Ireland or Israel.^[4] Some places have no common abbreviation at all, so the table shows a dash. When precision matters, use the offset for a moment in time, or the zone ID for a place. The UTC offset calculator shows any zone's offset on any date.

1. 1.MDN, Intl.supportedValuesOf(). Browsers listing the time zones they know.
2. 2.IANA, Time Zone Database. The zone IDs and their offsets and rules.
3. 3.Wikipedia, List of UTC offsets. Nearly 40 offsets in use, from UTC−12 to UTC+14.
4. 4.IANA, Theory and pragmatics of the tz code and data. How zone IDs are named, and why abbreviations are ambiguous.