Time zone abbreviations — what the letters actually mean
63 abbreviations, 5 of which mean more than one thing. CST is Central Standard Time in Chicago, China Standard Time in Shanghai and Cuba Standard Time in Havana — fourteen hours between the extremes and nothing in the letters to tell them apart. Every code here has its own page that reads a timestamp as all of its meanings at once, in your own clock.
63 of 63
- EST Eastern Standard Time The US and Canadian east coast in winter. UTC−05:00
- EDT Eastern Daylight Time The same places from March to November. UTC−04:00
- CST Central Standard Time The central United States, most of Mexico and central Canada in winter. UTC−06:00 ambiguous
- CDT Central Daylight Time The central United States and Canada from March to November. UTC−05:00
- MST Mountain Standard Time The US mountain states and Alberta. Arizona stays on it all year. UTC−07:00
- MDT Mountain Daylight Time The same, in summer — except Arizona, which does not change. UTC−06:00
- PST Pacific Standard Time The US and Canadian west coast in winter. UTC−08:00
- PDT Pacific Daylight Time The west coast from March to November — which is most of the year. UTC−07:00
- AKST Alaska Standard Time Alaska in winter. UTC−09:00
- AKDT Alaska Daylight Time Alaska in summer. UTC−08:00
- HST Hawaii Standard Time Hawaii, all year — it does not change the clocks. UTC−10:00
- AST Atlantic Standard Time Atlantic Canada and much of the Caribbean. UTC−04:00
- ADT Atlantic Daylight Time Atlantic Canada in summer. UTC−03:00
- NST Newfoundland Standard Time Newfoundland — half an hour off its neighbours. UTC−03:30
- NDT Newfoundland Daylight Time Newfoundland in summer. UTC−02:30
- BRT Brasília Time Most of Brazil. It stopped changing clocks in 2019. UTC−03:00
- ART Argentina Time Argentina, all year. UTC−03:00
- CLT Chile Standard Time Chile in its winter, which is the northern summer. UTC−04:00
- CLST Chile Summer Time Chile from September to April — its summer, which is the northern winter. UTC−03:00
- COT Colombia Time Colombia, all year. UTC−05:00
- PET Peru Time Peru, all year. UTC−05:00
- VET Venezuela Time Venezuela. It was −04:30 until 2016. UTC−04:00
- CST China Standard Time All of China, which runs one zone across five geographic ones. UTC+08:00 ambiguous
- CST Cuba Standard Time Cuba in winter. UTC−05:00 ambiguous
- IST India Standard Time All of India and Sri Lanka — half an hour off the grid. UTC+05:30 ambiguous
- IST Irish Standard Time Ireland in summer. Ireland is the odd case where the SUMMER time is the legally standard one. UTC+01:00 ambiguous
- IST Israel Standard Time Israel in winter. UTC+02:00 ambiguous
- AMT Amazon Time Western Brazil. UTC−04:00 ambiguous
- AMT Armenia Time Armenia — eight hours from the other AMT. UTC+04:00 ambiguous
- WST Western Standard Time Western Australia. UTC+08:00 ambiguous
- WST West Samoa Time Samoa, which is a day ahead of American Samoa next door. UTC+13:00 ambiguous
- BST British Summer Time The United Kingdom from late March to late October. UTC+01:00 ambiguous
- BST Bangladesh Standard Time Bangladesh, all year — five hours from the British one. UTC+06:00 ambiguous
- GMT Greenwich Mean Time The UK in winter, and West Africa all year. Not the same thing as UTC, though they agree to the second in practice. UTC+00:00
- UTC Coordinated Universal Time The reference every other zone is defined against. It never changes and belongs to no country. UTC+00:00
- WET Western European Time Portugal and the Canaries in winter. UTC+00:00
- WEST Western European Summer Time Portugal in summer. UTC+01:00
- CET Central European Time Most of continental Europe in winter, from Spain to Poland. UTC+01:00
- CEST Central European Summer Time The same countries from late March to late October. UTC+02:00
- EET Eastern European Time Finland, Greece, Romania, Egypt and the Baltics in winter. UTC+02:00
- EEST Eastern European Summer Time The same, in summer. UTC+03:00
- MSK Moscow Time Western Russia. It stopped changing clocks in 2014. UTC+03:00
- TRT Turkey Time Türkiye, all year since 2016. UTC+03:00
- WAT West Africa Time Nigeria, Cameroon and the DRC's west. UTC+01:00
- CAT Central Africa Time Zambia, Zimbabwe, Malawi and Mozambique. UTC+02:00
- EAT East Africa Time Kenya, Ethiopia, Tanzania and Somalia. UTC+03:00
- SAST South Africa Standard Time South Africa, all year. UTC+02:00
- GST Gulf Standard Time The UAE and Oman. UTC+04:00
- PKT Pakistan Standard Time Pakistan, all year. UTC+05:00
- NPT Nepal Time Nepal — 45 minutes off the hour, and one of only three zones that are. UTC+05:45
- ICT Indochina Time Thailand, Vietnam, Cambodia and Laos. UTC+07:00
- WIB Western Indonesian Time Java and Sumatra. UTC+07:00
- SGT Singapore Time Singapore, all year. UTC+08:00
- HKT Hong Kong Time Hong Kong, all year. UTC+08:00
- JST Japan Standard Time All of Japan. It has had no daylight saving since 1951. UTC+09:00
- KST Korea Standard Time South Korea, all year. UTC+09:00
- AWST Australian Western Standard Time Western Australia, all year. UTC+08:00
- ACST Australian Central Standard Time South Australia and the Northern Territory — nine and a half hours. UTC+09:30
- ACDT Australian Central Daylight Time South Australia in its summer. Darwin does not change. UTC+10:30
- AEST Australian Eastern Standard Time The Australian east coast. Queensland stays on it all year. UTC+10:00
- AEDT Australian Eastern Daylight Time Sydney and Melbourne from October to April — but not Brisbane. UTC+11:00
- NZST New Zealand Standard Time New Zealand in its winter. UTC+12:00
- NZDT New Zealand Daylight Time New Zealand from September to April. UTC+13:00
The ones that mean more than one thing
Ordered by how much a wrong guess costs. The number is the gap between the furthest-apart meanings.
- CST Central Standard Time · China Standard Time · Cuba Standard Time UTC−06:00 UTC+08:00 UTC−05:00 14 h apart
- AMT Amazon Time · Armenia Time UTC−04:00 UTC+04:00 8 h apart
- BST British Summer Time · Bangladesh Standard Time UTC+01:00 UTC+06:00 5 h apart
- WST Western Standard Time · West Samoa Time UTC+08:00 UTC+13:00 5 h apart
- IST India Standard Time · Irish Standard Time · Israel Standard Time UTC+05:30 UTC+01:00 UTC+02:00 4.5 h apart
Three letters, no authority
Time zone abbreviations feel official. They are printed on flight confirmations, stamped into log files and offered in dropdowns, which gives the impression that somebody somewhere maintains them. Nobody does. They came out of railway timetables and radio schedules, region by region, decades before anything needed to parse them mechanically, and by the time software cared the collisions were already fixed in habit.
The IANA time zone database — the one your operating system ships — records which abbreviations a zone uses, but it cannot resolve them the other way. Given the string CST there is no correct answer, only three candidates. Most software handles this by picking whichever meaning its locale suggests, silently. That is where the missed meetings come from: not from an error message, but from a confident wrong answer.
The half that is not ambiguous has a subtler trap. Almost every code names one side of the daylight-saving year: CET is the winter form and CEST the summer one, EST winter and EDT summer, GMT winter and BST summer. Writing CET for a date in July is not obviously broken — it parses, it produces a time, and that time is an hour out. Software that emits the abbreviation from a server's own locale rather than the event's makes this mistake constantly.
The fix costs nothing. Write the IANA zone name, or an ISO 8601 timestamp with a numeric offset. A zone name carries the rules and survives the clocks changing; a numeric offset is unambiguous for the instant it describes. Three letters are neither, however familiar they look.
How to use this
- Search by the letters, by the country, or by the offset — “india”, “+05:30” and “IST” all find the same row.
- The filters narrow to the ambiguous codes, the summer-time forms, or the ones that never change.
- Open any code to convert a timestamp written with it into your own clock.
Worth knowing: This list covers the abbreviations in common use, not every string that has ever been emitted. Some software invents its own; when in doubt, trust the numeric offset over the letters.
FAQ
Are time zone abbreviations standardised?
No. There is no registry and no authority. They grew up regionally in timetables and broadcasting, and several regions independently landed on the same three letters, which is why a handful of them are genuinely ambiguous today. The IANA time zone database records them but does not adjudicate between them.
Which abbreviations are ambiguous?
5 of the ones in common use: AMT, BST, CST, IST, WST. The worst is CST, whose meanings are 14 hours apart.
What should I write instead?
The IANA zone name — Europe/Oslo, America/New_York — or an ISO 8601 timestamp with a numeric offset such as 2026-03-14T15:00:00+01:00. The zone name is the stronger of the two because it carries the daylight-saving rules and not just today's number.
Why does my calendar show a different abbreviation in summer?
Because most abbreviations name one half of the year. CET becomes CEST, EST becomes EDT, GMT becomes BST. They are one hour apart and both correct, on the right dates, which is exactly why a timestamp labelled with the wrong half is an hour out rather than obviously broken.