Time zone abbreviations explained (EST, EDT, CET, UTC, GMT and more)
Time zone abbreviations look precise, but many of them are used wrongly or mean different things in different countries. Here is what the common ones mean and how to write times so nobody misreads them.
UTC and GMT
UTC (Coordinated Universal Time) is the global reference. It never changes for daylight saving time, which makes it useful for technical systems and aviation. GMT (Greenwich Mean Time) is, for everyday purposes, the same clock as UTC. The confusion is that the United Kingdom uses GMT only in winter; in summer it uses BST (British Summer Time, UTC+1). Saying "London time is GMT" is only true from late October to late March.
North America
| Abbreviation | Name | Offset | Used |
|---|---|---|---|
| EST / EDT | Eastern Standard / Daylight Time | UTC−5 / UTC−4 | New York, Miami, Toronto |
| CST / CDT | Central Standard / Daylight Time | UTC−6 / UTC−5 | Chicago, Houston, Dallas |
| MST / MDT | Mountain Standard / Daylight Time | UTC−7 / UTC−6 | Denver; Phoenix stays on MST all year |
| PST / PDT | Pacific Standard / Daylight Time | UTC−8 / UTC−7 | Los Angeles, Seattle, Vancouver |
| AST | Atlantic Standard Time | UTC−4 | Puerto Rico, Dominican Republic, Halifax (winter) |
The most common error is writing "EST" in summer. From March to November, the East Coast is on EDT. If you want a label that is always correct, write "ET" (Eastern Time) or simply "New York time".
Europe
| Abbreviation | Name | Offset | Used |
|---|---|---|---|
| GMT / BST | Greenwich Mean / British Summer Time | UTC+0 / UTC+1 | London; Dublin and Lisbon use the same clock |
| CET / CEST | Central European / Central European Summer Time | UTC+1 / UTC+2 | Madrid, Paris, Berlin, Rome, Amsterdam |
| EET / EEST | Eastern European / Summer Time | UTC+2 / UTC+3 | Athens, Helsinki, Bucharest, Kyiv |
The ambiguous ones
- CST means US Central Standard Time (UTC−6), China Standard Time (UTC+8) or Cuba Standard Time (UTC−5). A 14-hour difference hides behind the same three letters.
- IST can be India Standard Time (UTC+5:30), Irish Standard Time (UTC+1 in summer) or Israel Standard Time (UTC+2).
- BST is British Summer Time, but some people use it for Bangladesh Standard Time (UTC+6).
- AST is Atlantic Standard Time in the Americas and Arabia Standard Time (UTC+3) in the Gulf.
How to write times safely
- Use the city: "3:00 PM Madrid". Everyone understands it and it is correct all year.
- Or use the UTC offset for the specific date: "15:00 UTC+1". Precise, but people still need to convert.
- Use IANA names in software: "America/Bogota" or "Europe/Madrid". These are the identifiers that calendars and operating systems understand, and they include every historical rule change.
World Meeting Sync works with city names and IANA time zones behind the scenes, so the times shown already include daylight saving time for the date you pick. Search any city in the planner to see its current offset.