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Time zone abbreviations explained

PST. EST. IST. AEST. CET. GMT. There are dozens of three- or four-letter time zone abbreviations, several of which mean different things in different parts of the world. This page is a clear reference to the most common ones, including the few that are dangerously ambiguous — and the IANA names you should use instead in any technical context.

Heads up: "IST" can mean Indian Standard Time (UTC+5:30), Irish Standard Time (UTC+1) or Israel Standard Time (UTC+2). "CST" can mean US Central Standard Time, China Standard Time, or Cuba Standard Time. Use IANA names like Asia/Kolkata in code or anywhere precision matters.

North America

Abbr.	Name	UTC offset	DST
EST	Eastern Standard Time	UTC−5	No (winter only)
EDT	Eastern Daylight Time	UTC−4	Yes (summer)
CST	Central Standard Time	UTC−6	No (winter only)
CDT	Central Daylight Time	UTC−5	Yes (summer)
MST	Mountain Standard Time	UTC−7	No
MDT	Mountain Daylight Time	UTC−6	Yes
PST	Pacific Standard Time	UTC−8	No
PDT	Pacific Daylight Time	UTC−7	Yes
AKST/AKDT	Alaska Standard / Daylight	UTC−9 / −8	Yes
HST	Hawaii Standard Time	UTC−10	No DST
NST/NDT	Newfoundland	UTC−3:30 / −2:30	Yes
AST/ADT	Atlantic Standard / Daylight	UTC−4 / −3	Yes

Europe

Abbr.	Name	UTC offset	DST
GMT	Greenwich Mean Time	UTC+0	No (winter zone)
BST	British Summer Time	UTC+1	Yes
WET/WEST	Western European	UTC+0 / +1	Yes
CET	Central European Time	UTC+1	No (winter zone)
CEST	Central European Summer Time	UTC+2	Yes
EET	Eastern European Time	UTC+2	No (winter zone)
EEST	Eastern European Summer Time	UTC+3	Yes
MSK	Moscow Standard Time	UTC+3	No DST

Asia, Middle East and Africa

Abbr.	Name	UTC offset	DST
IST	India Standard Time	UTC+5:30	No
PKT	Pakistan Standard Time	UTC+5	No
BDT	Bangladesh Standard Time	UTC+6	No
SGT	Singapore Time	UTC+8	No
HKT	Hong Kong Time	UTC+8	No
CST	China Standard Time	UTC+8	No
JST	Japan Standard Time	UTC+9	No
KST	Korea Standard Time	UTC+9	No
GST	Gulf Standard Time	UTC+4	No
IRST/IRDT	Iran Standard / Daylight	UTC+3:30 / +4:30	Suspended 2022
SAST	South Africa Standard Time	UTC+2	No
EAT	East Africa Time	UTC+3	No

Australia, New Zealand and the Pacific

Abbr.	Name	UTC offset	DST
AEST	Australian Eastern Standard	UTC+10	No (winter zone)
AEDT	Australian Eastern Daylight	UTC+11	Yes
ACST	Australian Central Standard	UTC+9:30	No (winter)
ACDT	Australian Central Daylight	UTC+10:30	Yes
AWST	Australian Western Standard	UTC+8	No DST
NZST/NZDT	New Zealand Standard / Daylight	UTC+12 / +13	Yes

The dangerous ambiguities

IST. India (UTC+5:30), Ireland (UTC+1), Israel (UTC+2). Always state which IST you mean — or use Asia/Kolkata, Europe/Dublin or Asia/Jerusalem.
CST. US Central (UTC−6), China (UTC+8), Cuba (UTC−5). Mostly resolved by context but easy to misread.
EST. US Eastern (UTC−5), Australian Eastern Standard (UTC+10) is more often written AEST, but you'll occasionally see "EST" used for it informally. Confusion almost guaranteed.
BST. British Summer Time (UTC+1) or Bangladesh Standard Time (UTC+6, no longer in use).

Use IANA names where it counts

For software, calendars and any documentation that needs to survive future political changes, use the IANA time zone names. They are unambiguous, actively maintained, and supported by every modern operating system and programming language. Examples:

America/New_York, America/Los_Angeles, America/Chicago
Europe/London, Europe/Berlin, Europe/Paris
Asia/Kolkata, Asia/Tokyo, Asia/Singapore, Asia/Dubai
Australia/Sydney, Australia/Perth

FAQ

Why are some abbreviations the same as others?

Because abbreviations are coined locally and there is no global authority. Several IST, CST and EST exist for unrelated zones.

Are abbreviations case-sensitive?

Conventionally they're written in upper case, but tools accept either case. They are not case-sensitive in any standard.

What's the safest way to write a meeting time in an email?

Include the city and the date: "Tuesday 14:00 New York time". A reader can resolve that without any abbreviation knowledge.

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