Time zone abbreviations explained — EST, IST, PST, JST, GMT and more
If a colleague messages you "let's meet at 3 PM IST tomorrow," and you're an American who's never worked with India, your first reaction might be confusion. IST = Indian Standard Time? Israel Standard Time? Irish Standard Time? Iran Standard Time? It's all four, depending on context.
Time-zone abbreviations are a useful shortcut when context is clear and a source of bugs when it isn't. Here's the full reference.
For unambiguous conversions, the time converter uses full IANA zone names (`Asia/Kolkata` for India, etc.) which never have these ambiguities.
The most common abbreviations
Americas (UTC-3 to UTC-12)
| Abbreviation | Full name | Offset | Where |
|--------------|-----------|--------|-------|
| HST | Hawaii Standard Time | UTC-10 | Hawaii (no DST) |
| AKST/AKDT | Alaska Standard/Daylight | UTC-9/-8 | Alaska |
| PST/PDT | Pacific Standard/Daylight | UTC-8/-7 | US/Canada West |
| MST/MDT | Mountain Standard/Daylight | UTC-7/-6 | US/Canada Mountain |
| CST/CDT | Central Standard/Daylight | UTC-6/-5 | US/Canada Central |
| EST/EDT | Eastern Standard/Daylight | UTC-5/-4 | US/Canada East |
| AST/ADT | Atlantic Standard/Daylight | UTC-4/-3 | Canada Atlantic, Caribbean |
| NST/NDT | Newfoundland Standard/Daylight | UTC-3:30/-2:30 | Newfoundland |
| BRT | Brasília Time | UTC-3 | Brazil (most) |
| ART | Argentina Time | UTC-3 | Argentina |
Europe & Africa (UTC+0 to UTC+3)
| Abbreviation | Full name | Offset | Where |
|--------------|-----------|--------|-------|
| GMT/UTC | Greenwich Mean Time / UTC | UTC+0 | UK winter, reference |
| BST | British Summer Time | UTC+1 | UK summer |
| WET/WEST | Western European | UTC+0/+1 | Portugal, Ireland |
| CET/CEST | Central European | UTC+1/+2 | Most mainland Europe |
| EET/EEST | Eastern European | UTC+2/+3 | Eastern Europe |
| MSK | Moscow Time | UTC+3 | Russia (Moscow) |
| SAST | South African Standard | UTC+2 | South Africa (no DST) |
| CAT | Central Africa Time | UTC+2 | Central Africa |
| EAT | East Africa Time | UTC+3 | Kenya, Ethiopia, etc. |
Asia (UTC+3:30 to UTC+9)
| Abbreviation | Full name | Offset | Where |
|--------------|-----------|--------|-------|
| IRST | Iran Standard Time | UTC+3:30 | Iran (DST abolished 2022) |
| GST | Gulf Standard Time | UTC+4 | UAE, Oman |
| AFT | Afghanistan Time | UTC+4:30 | Afghanistan |
| PKT | Pakistan Standard Time | UTC+5 | Pakistan |
| IST | Indian Standard Time | UTC+5:30 | India, Sri Lanka |
| NPT | Nepal Time | UTC+5:45 | Nepal |
| BST | Bangladesh Standard Time | UTC+6 | Bangladesh (NOT British Summer Time!) |
| MMT | Myanmar Time | UTC+6:30 | Myanmar |
| ICT | Indochina Time | UTC+7 | Thailand, Vietnam, Cambodia |
| CST | China Standard Time | UTC+8 | China, Taiwan (NOT US Central!) |
| SGT | Singapore Time | UTC+8 | Singapore |
| HKT | Hong Kong Time | UTC+8 | Hong Kong |
| JST | Japan Standard Time | UTC+9 | Japan |
| KST | Korea Standard Time | UTC+9 | South Korea, North Korea |
Pacific & Australia
| Abbreviation | Full name | Offset | Where |
|--------------|-----------|--------|-------|
| AWST | Australian Western | UTC+8 | Western Australia |
| ACST/ACDT | Australian Central | UTC+9:30/+10:30 | South Australia |
| AEST/AEDT | Australian Eastern | UTC+10/+11 | Sydney, Melbourne |
| NZST/NZDT | New Zealand Standard/Daylight | UTC+12/+13 | New Zealand |
| SST | Samoa Standard Time | UTC-11 | American Samoa |
| HAST | Hawaii-Aleutian Standard | UTC-10 | Hawaii (less common) |
The ambiguous ones — be careful
These abbreviations have multiple meanings depending on context:
IST can mean:
- Indian Standard Time (UTC+5:30) — most common worldwide
- Israel Standard Time (UTC+2)
- Irish Standard Time (UTC+1, summer)
- Iran Standard Time (UTC+3:30, before 2022)
CST can mean:
- Central Standard Time (US, UTC-6) — most common in North America
- China Standard Time (UTC+8) — most common in Asia
- Cuba Standard Time (UTC-5)
BST can mean:
- British Summer Time (UK, UTC+1) — most common in UK/Europe
- Bangladesh Standard Time (UTC+6)
- Bougainville Standard Time (UTC+11)
AST can mean:
- Atlantic Standard Time (Canada/Caribbean, UTC-4)
- Arabia Standard Time (Saudi Arabia, UTC+3)
EST is mostly unambiguous (Eastern Standard Time, US/Canada, UTC-5) — but used loosely as a colloquial reference even outside that zone.
When to use abbreviations
Use them when:
- The audience is local. "Meeting at 3 PM EST" is fine on a US-only Slack channel.
- The context is unambiguous. "Tokyo team meeting at 9 AM JST" — JST has only one meaning.
Don't use them when:
- Mixing audiences. "Meeting at 9 AM IST" sent to a US/UK/India team will confuse half of them.
- Working across systems. Database column types, API parameters, log timestamps should use IANA names or UTC offsets, not abbreviations.
What to use instead
For unambiguous time-zone reference:
1. IANA zone names (`America/New_York`, `Asia/Kolkata`, `Europe/London`). Used by all modern software. Includes DST rules implicitly.
2. UTC offsets with date (`UTC+5:30 on 2026-05-21`). Specific and unambiguous, including DST.
3. Specific city + country. "9 AM Mumbai time" is clearer than "9 AM IST" if your audience might confuse IST.
For casual use among colleagues who all know the convention, abbreviations are fine.
A note on "EST" vs "ET" usage
Many news outlets and casual contexts use "ET" (Eastern Time) instead of EST or EDT. "ET" is a generic name covering both EST (winter) and EDT (summer) — it doesn't tell you which is currently in effect. This is convenient for general reference ("the deadline is 5 PM ET") but ambiguous for precise scheduling.
If you mean the specific UTC offset, use EST (winter) or EDT (summer). If you mean "wherever the East Coast is right now," use ET.
FAQ
Are time zone abbreviations standardized internationally?
No. They're conventional, not formal. Different countries use different abbreviations for the same offset. The IANA tz database is the closest thing to a global standard.
Why do some abbreviations conflict?
Each abbreviation was created independently within its country/region. By the time international communication became common, the conflicts were entrenched. Switching to IANA names is the modern solution.
What does "Z" mean in timestamps like "2026-05-10T14:30:00Z"?
Z = Zulu = UTC. It's the ISO 8601 designator for UTC. So that timestamp is 14:30 UTC on May 10, 2026.
Why is British Summer Time abbreviated BST instead of BST_UK or something unambiguous?
Pure historical accident. The UK adopted "British Summer Time" in 1916 and started using BST as the abbreviation. Bangladesh chose its abbreviation later, also picking BST. Conflict ensued.
How do I know which CST someone means?
Context. If they're in the US, it's almost certainly Central Standard Time (UTC-6). If they're in China, it's China Standard Time (UTC+8). If you're not sure, ask or check the time difference and figure it out.
Should I use UTC offsets in calendar invites?
Most modern calendar software shows the time in the recipient's local time anyway, so the abbreviation in the invite doesn't really matter — the calendar handles the conversion. But if you're sending a plain-text email about a meeting, prefer UTC ("17:00 UTC") to avoid ambiguity.
Bottom line
Time-zone abbreviations are a casual shortcut. For most everyday use within a single country or region, they're fine. For anything cross-region or in software, prefer IANA names (`Continent/City`) or UTC offsets with explicit dates.
The time converter handles all the abbreviations and IANA names you might encounter — paste a city or zone name and it figures out the rest.