Timezone Abbreviations
Reference table of common timezone abbreviations — UTC offset, DST status, IANA zone name, and the regions that use each one. Search by abbreviation, name, IANA zone, or region.
| Abbr. | Full Name | UTC Offset | DST ¹ | IANA Zone ² | Regions |
|---|---|---|---|---|---|
UTC | Coordinated Universal Time | +00:00 | — | UTC | Worldwide |
GMT | Greenwich Mean Time | +00:00 | — | Etc/GMT | UK, Ireland, West Africa, Iceland |
Z | Zulu Time (UTC+0) | +00:00 | — | UTC | Aviation, military, ISO 8601 |
HST | Hawaii Standard Time | −10:00 | — | Pacific/Honolulu | US (Hawaii) |
AKST | Alaska Standard Time | −09:00 | — | America/Anchorage | US (Alaska) |
AKDT | Alaska Daylight Time | −08:00 | Yes | America/Anchorage | US (Alaska) |
PST | Pacific Standard Time | −08:00 | — | America/Los_Angeles | US, Canada (Pacific) |
PDT | Pacific Daylight Time | −07:00 | Yes | America/Los_Angeles | US, Canada (Pacific) |
MST | Mountain Standard Time | −07:00 | — | America/Denver | US, Canada (Mountain) |
MDT | Mountain Daylight Time | −06:00 | Yes | America/Denver | US, Canada (Mountain) |
CST | Central Standard Time | −06:00 | — | America/Chicago | US, Canada (Central) |
CDT | Central Daylight Time | −05:00 | Yes | America/Chicago | US, Canada (Central) |
PET | Peru Time | −05:00 | — | America/Lima | Peru |
COT | Colombia Time | −05:00 | — | America/Bogota | Colombia |
EST | Eastern Standard Time | −05:00 | — | America/New_York | US, Canada (Eastern) |
EDT | Eastern Daylight Time | −04:00 | Yes | America/New_York | US, Canada (Eastern) |
CLT | Chile Standard Time | −04:00 | — | America/Santiago | Chile |
VET | Venezuela Time | −04:00 | — | America/Caracas | Venezuela |
AST | Atlantic Standard Time | −04:00 | — | America/Halifax | Canada (Atlantic), Caribbean |
ADT | Atlantic Daylight Time | −03:00 | Yes | America/Halifax | Canada (Atlantic) |
ART | Argentina Time | −03:00 | — | America/Argentina/Buenos_Aires | Argentina |
BRT | Brasília Time | −03:00 | — | America/Sao_Paulo | Brazil |
NST | Newfoundland Standard Time | −03:30 | — | America/St_Johns | Canada (Newfoundland) |
NDT | Newfoundland Daylight Time | −02:30 | Yes | America/St_Johns | Canada (Newfoundland) |
WET | Western European Time | +00:00 | — | Europe/Lisbon | Portugal, Faroe Islands |
WEST | Western European Summer Time | +01:00 | Yes | Europe/Lisbon | Portugal, Faroe Islands |
BST | British Summer Time | +01:00 | Yes | Europe/London | UK |
IST | Irish Standard Time | +01:00 | Yes | Europe/Dublin | Ireland |
WAT | West Africa Time | +01:00 | — | Africa/Lagos | West and Central Africa |
CET | Central European Time | +01:00 | — | Europe/Paris | Most of Europe (winter) |
CEST | Central European Summer Time | +02:00 | Yes | Europe/Paris | Most of Europe (summer) |
CAT | Central Africa Time | +02:00 | — | Africa/Johannesburg | Central and Southern Africa |
SAST | South Africa Standard Time | +02:00 | — | Africa/Johannesburg | South Africa, Zimbabwe |
EET | Eastern European Time | +02:00 | — | Europe/Helsinki | Eastern Europe (winter) |
IST | Israel Standard Time | +02:00 | — | Asia/Jerusalem | Israel |
EEST | Eastern European Summer Time | +03:00 | Yes | Europe/Helsinki | Eastern Europe (summer) |
EAT | East Africa Time | +03:00 | — | Africa/Nairobi | East Africa |
MSK | Moscow Standard Time | +03:00 | — | Europe/Moscow | Russia (Moscow) |
TRT | Turkey Time | +03:00 | — | Europe/Istanbul | Turkey |
IDT | Israel Daylight Time | +03:00 | Yes | Asia/Jerusalem | Israel |
AST | Arabia Standard Time | +03:00 | — | Asia/Riyadh | Saudi Arabia, Kuwait, Iraq |
GST | Gulf Standard Time | +04:00 | — | Asia/Dubai | UAE, Oman, Bahrain |
AFT | Afghanistan Time | +04:30 | — | Asia/Kabul | Afghanistan |
PKT | Pakistan Standard Time | +05:00 | — | Asia/Karachi | Pakistan |
IST | India Standard Time | +05:30 | — | Asia/Kolkata | India, Sri Lanka |
NPT | Nepal Time | +05:45 | — | Asia/Kathmandu | Nepal |
BST | Bangladesh Standard Time | +06:00 | — | Asia/Dhaka | Bangladesh |
MMT | Myanmar Time | +06:30 | — | Asia/Rangoon | Myanmar |
IRST | Iran Standard Time | +03:30 | — | Asia/Tehran | Iran |
IRDT | Iran Daylight Time | +04:30 | Yes | Asia/Tehran | Iran |
ICT | Indochina Time | +07:00 | — | Asia/Bangkok | Thailand, Vietnam, Cambodia, Laos |
WIB | Western Indonesia Time | +07:00 | — | Asia/Jakarta | Western Indonesia |
WITA | Central Indonesia Time | +08:00 | — | Asia/Makassar | Central Indonesia |
WIT | Eastern Indonesia Time | +09:00 | — | Asia/Jayapura | Eastern Indonesia |
SGT | Singapore Standard Time | +08:00 | — | Asia/Singapore | Singapore, Malaysia |
SST | Singapore Standard Time | +08:00 | — | Asia/Singapore | Singapore |
HKT | Hong Kong Time | +08:00 | — | Asia/Hong_Kong | Hong Kong |
CST | China Standard Time | +08:00 | — | Asia/Shanghai | China, Taiwan |
PHT | Philippine Time | +08:00 | — | Asia/Manila | Philippines |
AWST | Australian Western Standard Time | +08:00 | — | Australia/Perth | Australia (Western Australia) |
JST | Japan Standard Time | +09:00 | — | Asia/Tokyo | Japan |
KST | Korea Standard Time | +09:00 | — | Asia/Seoul | South Korea, North Korea |
ACST | Australian Central Standard Time | +09:30 | — | Australia/Darwin | Australia (NT, SA) |
SST | Samoa Standard Time | −11:00 | — | Pacific/Pago_Pago | Samoa, American Samoa |
AEST | Australian Eastern Standard Time | +10:00 | — | Australia/Brisbane | Australia (QLD, Eastern states) |
ACDT | Australian Central Daylight Time | +10:30 | Yes | Australia/Adelaide | Australia (SA) |
AEDT | Australian Eastern Daylight Time | +11:00 | Yes | Australia/Sydney | Australia (NSW, VIC, TAS, ACT) |
NZST | New Zealand Standard Time | +12:00 | — | Pacific/Auckland | New Zealand |
NZDT | New Zealand Daylight Time | +13:00 | Yes | Pacific/Auckland | New Zealand |
¹ DST — Daylight Saving Time: clocks advance by 1 hour in spring and fall back in autumn. Paired abbreviations share the same IANA zone (e.g. EST ↔ EDT → America/New_York).
² IANA Zone — representative zone from the IANA tz database. Ambiguous abbreviations map to multiple IANA zones — always use the full IANA name in code, never the abbreviation.
Key terms
- UTC — Coordinated Universal Time
- The primary international time standard since 1972. UTC never changes for Daylight Saving and serves as the zero-offset baseline from which all other timezones are measured. Servers, databases, and APIs store times in UTC to avoid ambiguity.
- GMT — Greenwich Mean Time
- The time at the Royal Observatory in Greenwich, London. In practice, GMT and UTC are the same offset (+00:00). The difference is technical: GMT is an astronomical standard while UTC is an atomic standard. Modern systems use UTC; GMT appears in older HTTP headers and email standards.
- DST — Daylight Saving Time
- The practice of advancing clocks by one hour in spring ('spring forward') and setting them back in autumn ('fall back'), to shift daylight into the evening. Not universal — Japan, China, India, and most of Africa don't observe it. DST transitions are a leading cause of timestamp bugs in software.
- IANA timezone name
- A unique identifier from the IANA tz database that names a timezone region unambiguously, including all its DST rules. Examples: America/New_York, Europe/London, Asia/Kolkata. Always prefer IANA names over short abbreviations in code.
Why abbreviations are ambiguous
Timezone abbreviations grew organically — there is no single authority that assigns them. As a result, the same string can mean completely different things depending on the region. IST is the most extreme case: it is used independently by India, Ireland, and Israel, spanning a range of four and a half hours.
CST is used for US Central Standard Time (UTC−6) and China Standard Time (UTC+8) — a 14-hour difference. SST means both Singapore Standard Time (UTC+8) and Samoa Standard Time (UTC−11) — a 19-hour gap. AST means Atlantic Standard Time (UTC−4) in Canada and Arabia Standard Time (UTC+3) in the Middle East.
For any production code, use IANA timezone names from the tz database — the Timezone Converter above uses them to keep every zone’s DST rules correct. Most languages expose them natively: Intl.DateTimeFormat().resolvedOptions().timeZone in JavaScript, ZoneId.systemDefault() in Java, or time.LoadLocation in Go.
Frequently asked questions
What does IST stand for in timezones?
IST is ambiguous — it stands for India Standard Time (UTC+5:30), Irish Standard Time (UTC+1, DST), and Israel Standard Time (UTC+2). Because of this, IANA timezone names like Asia/Kolkata, Europe/Dublin, or Asia/Jerusalem should always be used in code.
What is the difference between EST and EDT?
EST (Eastern Standard Time) is UTC−5 and is used in the US and Canada during winter. EDT (Eastern Daylight Time) is UTC−4 and is used during summer when clocks move forward by one hour. Both map to the IANA zone America/New_York, which handles the transition automatically.
What does CST stand for?
CST is ambiguous: it means US Central Standard Time (UTC−6) in North America, and China Standard Time (UTC+8) in Asia — a 14-hour difference. Always confirm from context which one is meant, or use the IANA name: America/Chicago vs Asia/Shanghai.
What is Daylight Saving Time (DST)?
Daylight Saving Time is the practice of advancing clocks by one hour during summer months to make better use of daylight. Clocks 'spring forward' in spring and 'fall back' in autumn. Not all countries or regions observe DST — Japan, China, India, and most of Africa do not.
Why are timezone abbreviations unreliable in code?
Many abbreviations are shared by multiple timezones (IST, CST, BST, AST, SST). They also don't encode DST transitions — code using raw abbreviations will produce incorrect results when the clock changes. Use IANA timezone names instead.
What is the IANA timezone database?
The IANA timezone database (also called the Olson database, or tz database) is the authoritative source of timezone rules for every region in the world. It uses names like America/Chicago, Europe/Paris, and Pacific/Auckland. It is updated several times per year as governments change their DST rules.