Time Zone Abbreviations Explained — EST, PST, GMT, KST, CET and the Traps
Three-letter zone codes look precise, but several of them mean completely different things on different continents, and half of them silently change with the season. Here's what the common ones mean — and why professionals write city names or UTC offsets instead.
The two things abbreviations hide
Before the tables, the two systematic problems:
- They're not unique. Nobody owns these codes — they're informal conventions, so the same three letters were invented independently in different countries. "CST" is used for zones eight and fourteen hours apart.
- Standard vs daylight pairs. In regions with daylight saving time, each zone has two codes: EST (UTC−5) in winter becomes EDT (UTC−4) in summer. Writing "EST" in July is technically wrong and, worse, ambiguous — did the writer mean literal UTC−5, or just "New York time"?
North America
| Code | Name | Offset | Summer code | Main cities |
|---|---|---|---|---|
| EST | Eastern Standard Time | UTC−5 | EDT (UTC−4) | New York, Toronto, Miami |
| CST | Central Standard Time | UTC−6 | CDT (UTC−5) | Chicago, Dallas, Mexico City* |
| MST | Mountain Standard Time | UTC−7 | MDT (UTC−6) | Denver; Phoenix stays on MST all year |
| PST | Pacific Standard Time | UTC−8 | PDT (UTC−7) | Los Angeles, San Francisco, Vancouver |
| AKST | Alaska Standard Time | UTC−9 | AKDT (UTC−8) | Anchorage |
| HST | Hawaii Standard Time | UTC−10 | — (no DST) | Honolulu |
*Mexico City abolished DST in 2022, so it stays on UTC−6 year-round even while US Central cities shift.
Europe
| Code | Name | Offset | Summer code | Main cities |
|---|---|---|---|---|
| GMT | Greenwich Mean Time | UTC+0 | BST (UTC+1) | London, Dublin, Lisbon |
| WET | Western European Time | UTC+0 | WEST (UTC+1) | Lisbon, Canary Islands |
| CET | Central European Time | UTC+1 | CEST (UTC+2) | Paris, Berlin, Madrid, Rome, Warsaw |
| EET | Eastern European Time | UTC+2 | EEST (UTC+3) | Athens, Helsinki, Kyiv, Bucharest |
| MSK | Moscow Time | UTC+3 | — (no DST) | Moscow, St. Petersburg |
Note that GMT and UTC show the same time in practice, but they're conceptually different things — see UTC vs GMT.
Asia and Oceania
| Code | Name | Offset | Notes |
|---|---|---|---|
| IST | India Standard Time | UTC+5:30 | No DST; the famous half-hour offset |
| ICT | Indochina Time | UTC+7 | Bangkok, Hanoi; Jakarta uses WIB (also +7) |
| CST | China Standard Time | UTC+8 | Beijing, Shanghai — one zone for the whole country |
| SGT / HKT | Singapore / Hong Kong Time | UTC+8 | No DST |
| KST | Korea Standard Time | UTC+9 | Seoul; no DST |
| JST | Japan Standard Time | UTC+9 | Tokyo; no DST |
| AWST | Australian Western Standard Time | UTC+8 | Perth; no DST |
| ACST | Australian Central Standard Time | UTC+9:30 | Adelaide → ACDT (UTC+10:30) in southern summer |
| AEST | Australian Eastern Standard Time | UTC+10 | Sydney, Melbourne → AEDT (UTC+11); Brisbane stays AEST |
| NZST | New Zealand Standard Time | UTC+12 | Auckland → NZDT (UTC+13) in southern summer |
The dangerous ones: same letters, different planets
- CST — Central Standard Time (UTC−6, Chicago), China Standard Time (UTC+8, Beijing), and Cuba Standard Time (UTC−5, Havana). A "3 PM CST" between a US and a Chinese team can be read fourteen hours apart.
- IST — India Standard Time (UTC+5:30), Israel Standard Time (UTC+2), and Irish Standard Time (UTC+1, and it's Ireland's summer time despite the name).
- BST — British Summer Time (UTC+1) but also Bangladesh Standard Time (UTC+6).
- EST / EDT confusion — people habitually write "EST" year-round for US Eastern time; in summer the zone is actually EDT. Most readers auto-correct, but automated systems and literal-minded colleagues won't.
What to write instead
- Best: a city. "18:00 Seoul time" is unambiguous forever — the city pins down the IANA zone and all its DST rules. This is what calendar systems do internally (
Asia/Seoul,America/New_York). - Good: an explicit UTC offset. "18:00 UTC+9" can't be misread, though unlike a city it won't follow a DST change.
- For aviation, military, and servers: Zulu. "1500Z" means 15:00 UTC — the Z suffix is the one abbreviation that is genuinely unambiguous.
- Acceptable: abbreviation + one anchor city. If your audience expects "PST", write "9 AM PT (Los Angeles)" so any confusion self-corrects.
Check any code against a live clock
If someone sends you a time in an abbreviation you're unsure about, don't guess: pin the sender's city on the gworldtime globe and read the live time and offset directly. It's faster than looking up the code and immune to the CST/IST traps above.
Read next: UTC vs GMT — what's the difference? · How time zones work · Scheduling meetings across time zones