Time zone abbreviations decoded
Including the ones that mean two different things — CST is fourteen hours wide depending on which country you assume.
The short answer
Abbreviations are not standardised, not unique, and not stable through the year. CST means US Central, China Standard and Cuba Standard Time. IST means India, Ireland and Israel.
Use a city name instead. That is what the time zone database itself does.
The ambiguous ones
| Code | Could mean | Offset |
|---|---|---|
| CST | Central Standard Time (US) | UTC−6 |
| China Standard Time | UTC+8 | |
| Cuba Standard Time | UTC−5 | |
| IST | India Standard Time | UTC+5:30 |
| Irish Standard Time | UTC+1 | |
| Israel Standard Time | UTC+2 | |
| BST | British Summer Time | UTC+1 |
| Bangladesh Standard Time | UTC+6 | |
| AMT | Amazon Time | UTC−4 |
| Armenia Time | UTC+4 | |
| ECT | Ecuador Time | UTC−5 |
| Central European Time | UTC+1 |
US Central and China Standard Time are fourteen hours apart under identical letters. That is not a subtle failure mode.
The common unambiguous ones
| Code | Meaning | Offset |
|---|---|---|
| UTC | Coordinated Universal Time | +0 |
| GMT | Greenwich Mean Time | +0 |
| EST / EDT | US Eastern standard / daylight | −5 / −4 |
| CDT | US Central daylight | −5 |
| MST / MDT | US Mountain standard / daylight | −7 / −6 |
| PST / PDT | US Pacific standard / daylight | −8 / −7 |
| CET / CEST | Central European standard / summer | +1 / +2 |
| EET / EEST | Eastern European standard / summer | +2 / +3 |
| JST | Japan Standard Time | +9 |
| KST | Korea Standard Time | +9 |
| AEST / AEDT | Australian Eastern standard / daylight | +10 / +11 |
| NZST / NZDT | New Zealand standard / daylight | +12 / +13 |
The seasonal trap, on top of the ambiguity
Even unambiguous codes are only correct half the year. EST is right in winter and wrong in summer, when the zone is on EDT. Same for CET/CEST, AEST/AEDT and the rest of the pairs.
So a code can fail in two independent ways: it can name the wrong country, and it can name the wrong season. "CST" in July, read by someone in Shanghai, manages both.
What to use instead
City names. "Chicago," "Shanghai," "Mumbai." Unambiguous, correct on every date, and understood without a lookup table.
IANA identifiers for anything technical: America/Chicago, Asia/Shanghai,
Asia/Kolkata. This is what your devices already use internally.
UTC offsets with a date if you must give a number: "UTC+8 on 14 March."
UTC timestamps for anything machine-read.
Why the database uses cities
The IANA time zone database deliberately identifies zones as Area/City rather
than by abbreviation, precisely because abbreviations collide and change.
The city is a label for a set of rules, not a geographic claim — everyone in
the US eastern zone is America/New_York whether they are in Miami or Toronto.
It is stable, unique, and it carries the full history of that zone's rule
changes.
Related: What time zone am I in? · EST vs EDT · The tz database
Timezone: World Clock Widget
A world clock, converter and live day/night map for iPhone — 325 cities, offline, no account.
Figures on this page are computed from the IANA time zone database. Last generated 2026-08-18.