Time Zone Abbreviations
A reference guide to 56 common time zone abbreviations — UTC offsets, DST variants, representative cities, and links to conversion pages. Several abbreviations are shared by multiple regions; those are flagged and explained below.
For precise scheduling, always use city names or IANA identifiers (e.g. America/New_York) rather than abbreviations. Abbreviations are convenient shorthands but can be ambiguous — IST alone could mean India, Ireland, or Israel.
Common Sources of Confusion
EST vs EDT
EST (Eastern Standard Time, UTC-5) is used by New York, Toronto, and Washington DC from November to March. When clocks spring forward in March, the zone switches to EDT (Eastern Daylight Time, UTC-4). Many people say 'EST' year-round, but technically the correct abbreviation during summer is EDT. Scheduling tools and calendar apps should always use the IANA identifier America/New_York rather than a fixed abbreviation to avoid off-by-one-hour errors.
PST vs PDT
PST (Pacific Standard Time, UTC−8) applies to Los Angeles, San Francisco and Seattle from November to March. In summer the zone shifts to PDT (Pacific Daylight Time, UTC−7). The gap between EST and PST is always 3 hours; the gap between EDT and PDT is also always 3 hours — New York and Los Angeles normally keep that three-hour gap across seasons. Their clock changes occur on the same dates at different instants, creating brief exceptions during the changeover hours, not a multi-week mismatch.
CST ambiguity — three zones, one abbreviation
CST is used for three completely different time zones: US Central Standard Time (UTC−6, Chicago), China Standard Time (UTC+8, Shanghai), and Cuba Standard Time (UTC−5, Havana). The 14-hour difference between US CST and China CST makes this ambiguity genuinely dangerous for scheduling. Always confirm which CST a colleague means — or better, use city names or IANA identifiers.
IST ambiguity — India, Ireland, and Israel
IST stands for India Standard Time (UTC+5:30), Irish Standard Time (UTC+1 in summer), and Israel Standard Time (UTC+2). India's IST is the most common globally. Ireland uses a quirky 'negative DST' model where GMT is the winter offset and IST is the summer offset — the reverse of most DST conventions. Israel uses IDT (Israel Daylight Time, UTC+3) in summer. When someone says 'IST' without context, confirm whether they mean Kolkata, Dublin, or Jerusalem.
GMT vs UTC — same offset, different standards
GMT (Greenwich Mean Time) and UTC (Coordinated Universal Time) both sit at UTC+0, but they are technically distinct. UTC is an atomic-clock-based international standard used by computers, APIs, and databases. GMT is a timezone used by the UK in winter (switching to BST in summer). For programming and data storage, always use UTC. For human communication involving London, GMT is correct in winter and BST in summer.
Full Abbreviation Reference
North America
| Abbr | Full Name | Offset | City / Region | Converter |
|---|---|---|---|---|
| EST | Eastern Standard Time | UTC−5 | New York | EST→PST |
| EDT | Eastern Daylight TimeDST | UTC−4 | New York | — |
| CSTambiguous | Central Standard Time (US) | UTC−6 | Chicago | CST→EST |
| CDT | Central Daylight TimeDST | UTC−5 | Chicago | — |
| MST | Mountain Standard Time | UTC−7 | Denver | MST→EST |
| MDT | Mountain Daylight TimeDST | UTC−6 | Denver | — |
| PST | Pacific Standard Time | UTC−8 | Los Angeles | PST→EST |
| PDT | Pacific Daylight TimeDST | UTC−7 | Los Angeles | — |
| AKST | Alaska Standard Time | UTC−9 | Anchorage | — |
| AKDT | Alaska Daylight TimeDST | UTC−8 | Anchorage | — |
| HST | Hawaii Standard Time | UTC−10 | Honolulu | — |
| AST | Atlantic Standard Time | UTC−4 | Halifax | — |
| ADT | Atlantic Daylight TimeDST | UTC−3 | Halifax | — |
| NST | Newfoundland Standard Time | UTC−3:30 | St. John's | — |
| NDT | Newfoundland Daylight TimeDST | UTC−2:30 | St. John's | — |
| BRT | Brasilia Time | UTC−3 | São Paulo | — |
| ART | Argentina Time | UTC−3 | Buenos Aires | — |
Europe
| Abbr | Full Name | Offset | City / Region | Converter |
|---|---|---|---|---|
| UTC | Coordinated Universal Time | UTC±0 | Universal | UTC→EST |
| GMTambiguous | Greenwich Mean Time | UTC±0 | London | GMT→EST |
| BST | British Summer TimeDST | UTC+1 | London | — |
| WET | Western European Time | UTC±0 | Lisbon | — |
| WEST | Western European Summer TimeDST | UTC+1 | Lisbon | — |
| CET | Central European Time | UTC+1 | Paris / Berlin | CET→EST |
| CEST | Central European Summer TimeDST | UTC+2 | Paris / Berlin | — |
| EET | Eastern European Time | UTC+2 | Helsinki / Athens | — |
| EEST | Eastern European Summer TimeDST | UTC+3 | Helsinki / Athens | — |
| MSK | Moscow Standard Time | UTC+3 | Moscow | — |
| ISTambiguous | Irish Standard TimeDST | UTC+1 | Dublin | — |
Africa & Middle East
| Abbr | Full Name | Offset | City / Region | Converter |
|---|---|---|---|---|
| WAT | West Africa Time | UTC+1 | Lagos | — |
| CAT | Central Africa Time | UTC+2 | Johannesburg | — |
| SAST | South Africa Standard Time | UTC+2 | Johannesburg | — |
| EAT | East Africa Time | UTC+3 | Nairobi | — |
| GST | Gulf Standard Time | UTC+4 | Dubai | — |
| ASTambiguous | Arabia Standard Time | UTC+3 | Riyadh | — |
Asia
| Abbr | Full Name | Offset | City / Region | Converter |
|---|---|---|---|---|
| PKT | Pakistan Standard Time | UTC+5 | Karachi | — |
| ISTambiguous | India Standard Time | UTC+5:30 | Kolkata / Mumbai | IST→EST |
| BSTambiguous | Bangladesh Standard Time | UTC+6 | Dhaka | — |
| ICT | Indochina Time | UTC+7 | Bangkok | — |
| CSTambiguous | China Standard Time | UTC+8 | Shanghai | — |
| SGT | Singapore Standard Time | UTC+8 | Singapore | — |
| HKT | Hong Kong Time | UTC+8 | Hong Kong | — |
| ISTambiguous | Israel Standard Time | UTC+2 | Jerusalem | — |
| IDT | Israel Daylight TimeDST | UTC+3 | Jerusalem | — |
| KST | Korea Standard Time | UTC+9 | Seoul | — |
| JST | Japan Standard Time | UTC+9 | Tokyo | PST→JST |
| WIB | Western Indonesia Time | UTC+7 | Jakarta | — |
| WITA | Central Indonesia Time | UTC+8 | Makassar | — |
| WIT | Eastern Indonesia Time | UTC+9 | Jayapura | — |
Pacific & Australia
| Abbr | Full Name | Offset | City / Region | Converter |
|---|---|---|---|---|
| AWST | Australian Western Standard Time | UTC+8 | Perth | — |
| ACST | Australian Central Standard Time | UTC+9:30 | Adelaide / Darwin | — |
| ACDT | Australian Central Daylight TimeDST | UTC+10:30 | Adelaide | — |
| AEST | Australian Eastern Standard Time | UTC+10 | Sydney / Melbourne | — |
| AEDT | Australian Eastern Daylight TimeDST | UTC+11 | Sydney / Melbourne | — |
| NZST | New Zealand Standard Time | UTC+12 | Auckland | — |
| NZDT | New Zealand Daylight TimeDST | UTC+13 | Auckland | — |
| CHAST | Chatham Standard Time | UTC+12:45 | Chatham Islands | — |
Frequently Asked Questions
- What is the difference between EST and EDT?
- EST (Eastern Standard Time) is UTC-5 and applies from November to March. EDT (Eastern Daylight Time) is UTC-4 and applies from March to November when clocks spring forward. Many people say 'EST' year-round but the correct summer abbreviation is EDT.
- What does CST stand for?
- CST can mean US Central Standard Time (UTC−6, Chicago), China Standard Time (UTC+8, Shanghai), or Cuba Standard Time (UTC−5, Havana). Always confirm which CST is meant, as the US and China interpretations differ by 14 hours.
- What is the difference between GMT and UTC?
- GMT and UTC both sit at UTC+0, but UTC is an atomic-clock-based international standard used in computing, while GMT is a timezone used by the UK in winter (switching to BST in summer). For programming always use UTC; for human communication involving London, GMT is correct in winter.
- What does IST stand for?
- IST stands for India Standard Time (UTC+5:30), Irish Standard Time (UTC+1 in summer), or Israel Standard Time (UTC+2). India Standard Time is the most common usage globally. Always confirm the region when IST is used without context.
Fact card
- Reference:
- Time zone abbreviations and UTC offsets
- Data source:
- IANA tz database (tzdata)
- DST note:
- Abbreviations like EST, PST, and GMT are winter-only labels — the same regions switch to EDT, PDT, and BST in summer. Offsets shown are standard-time values; live offsets on converter pages reflect the actual current abbreviation.
- Scope:
- 56 abbreviations across North America, Europe, Asia-Pacific, and Middle East