Time Zones · Reference
Time Zone Abbreviations: The Complete Reference (EST, PST, CET)
EST, PST, CET, IST — the three-letter codes are everywhere, and at least two of them mean more than one thing. Here's every common abbreviation, its UTC offset, and the trap to watch for before you schedule anything across them.
Key takeaways
- A time zone abbreviation like EST or CET is shorthand for a named zone, not a fixed offset — most shift by an hour when daylight saving starts or ends.
- The middle letter usually signals the season: Standard or Daylight, so
ESTbecomesEDTandCSTbecomesCDT. - Some abbreviations are genuinely ambiguous: CST can mean Central Standard Time (UTC−6) or China Standard Time (UTC+8) — a fourteen-hour gap.
- Because of that ambiguity, abbreviations aren't reliable for scheduling across time zones — a UTC offset or full location name says exactly what you mean.
- This reference is organized by region: North America, Europe, and Asia-Pacific, followed by the abbreviations most likely to be misread.
A colleague messages you: "Let's talk at 9am CST." Simple enough — unless you don't know whether they mean Central Standard Time in Chicago or China Standard Time in Shanghai, two zones fourteen hours apart. Time zone abbreviations are everywhere, from flight itineraries to calendar invites to the corner of a weather app, and most people use them without ever checking what the letters are actually promising.
This is the complete reference: every commonly used abbreviation, grouped by region, with its full name and current UTC offset, plus the handful that genuinely mean two different things depending on who's writing them. If you already know which abbreviation you're dealing with and just need the offset, the searchable abbreviations chart looks it up instantly.
01What is a time zone abbreviation?
A time zone abbreviation is a short label — usually two to five letters — that stands in for the full name of a named time zone, such as EST for Eastern Standard Time or CET for Central European Time. Unlike UTC, which is a single, precisely defined global reference, there's no single international authority assigning these abbreviations — they've grown up regionally, which is exactly why some of them overlap.
The abbreviation names the zone; it's the UTC offset that actually pins it to a specific number of hours. When someone writes "3:00 PM EST," what they're really specifying is "3:00 PM, UTC−5" — the letters are just a familiar substitute for that number.
02How abbreviations are built
Most Western abbreviations follow the same pattern: a region name, a status word, and "Time." Eastern Standard Time becomes EST; when daylight saving is in effect, "Standard" is swapped for "Daylight," giving EDT. The same pattern holds for CST/CDT, MST/MDT, and PST/PDT across North America.
Europe follows a similar shape but swaps the second word for "Summer" rather than "Daylight" — Central European Time, CET, becomes Central European Summer Time, CEST, in warmer months. Asia-Pacific zones more often skip the standard/daylight distinction altogether, since most of the region doesn't observe daylight saving at all.
The letter change isn't cosmetic
When the middle letter flips from S to D (or C to CS in Europe's pattern), the underlying offset genuinely moves — typically by one hour. The full mechanics of when that switch happens and why is covered in our guide to how daylight saving time works.
03North American abbreviations
North America has the most standard/daylight pairs of any region, running from Hawaii in the west to Newfoundland in the east.
| Abbrev. | Full name | UTC offset | Where it's used |
|---|---|---|---|
| HST | Hawaii Standard Time | UTC−10 | Hawaii (no daylight saving observed) |
| AKST / AKDT | Alaska Standard / Daylight Time | UTC−9 / UTC−8 | Alaska |
| PST / PDT | Pacific Standard / Daylight Time | UTC−8 / UTC−7 | US & Canadian west coast |
| MST / MDT | Mountain Standard / Daylight Time | UTC−7 / UTC−6 | US Mountain states (Arizona stays on MST year-round) |
| CST / CDT | Central Standard / Daylight Time | UTC−6 / UTC−5 | US Midwest & South, central Canada |
| EST / EDT | Eastern Standard / Daylight Time | UTC−5 / UTC−4 | US East Coast, eastern Canada |
| AST / ADT | Atlantic Standard / Daylight Time | UTC−4 / UTC−3 | Atlantic Canada |
| NST / NDT | Newfoundland Standard / Daylight Time | UTC−3:30 / UTC−2:30 | Newfoundland, Canada |
04European & UK abbreviations
Europe's zones run in one-hour bands from west to east, each with its own summer variant.
| Abbrev. | Full name | UTC offset | Where it's used |
|---|---|---|---|
| GMT / BST | Greenwich Mean Time / British Summer Time | UTC+0 / UTC+1 | United Kingdom, Ireland |
| WET / WEST | Western European Time / Summer Time | UTC+0 / UTC+1 | Portugal, parts of Spain & Morocco |
| CET / CEST | Central European Time / Summer Time | UTC+1 / UTC+2 | Most of continental Europe |
| EET / EEST | Eastern European Time / Summer Time | UTC+2 / UTC+3 | Finland, Greece, Romania, Ukraine |
GMT and UTC are frequently used as if they're the same thing, and for reading a clock they usually are — but they're defined differently underneath. See our UTC vs GMT comparison if you need the precise distinction.
05Asia-Pacific & other major zones
Most of Asia doesn't observe daylight saving, so these zones keep a single offset all year. Australia and New Zealand are the exceptions, switching between standard and daylight like North America.
| Abbrev. | Full name | UTC offset | Where it's used |
|---|---|---|---|
| PKT | Pakistan Standard Time | UTC+5 | Pakistan (no daylight saving observed) |
| IST | India Standard Time | UTC+5:30 | India (no daylight saving observed) |
| CST | China Standard Time | UTC+8 | China (no daylight saving observed) |
| JST | Japan Standard Time | UTC+9 | Japan (no daylight saving observed) |
| KST | Korea Standard Time | UTC+9 | South Korea (no daylight saving observed) |
| AEST / AEDT | Australian Eastern Standard / Daylight Time | UTC+10 / UTC+11 | Sydney, Melbourne, Brisbane (Queensland stays on AEST) |
| NZST / NZDT | New Zealand Standard / Daylight Time | UTC+12 / UTC+13 | New Zealand |
06When the same letters mean two things
The trap worth remembering
A handful of abbreviations are used, unrelated, in more than one part of the world. Reading the letters alone won't tell you which one someone means — you need the context or the region they're writing from.
| Abbrev. | Meaning #1 | Meaning #2 |
|---|---|---|
| CST | Central Standard Time (North America), UTC−6 | China Standard Time, UTC+8 |
| IST | India Standard Time, UTC+5:30 | Irish Standard Time, UTC+1 |
Both pairs are off by several hours, so guessing wrong doesn't just miss a meeting by a little — it can put you on the wrong day entirely.
07Military and aviation zone letters
Alongside the region-based abbreviations above, aviation and the military use a completely different, single-letter system. Every time zone on Earth is assigned one letter: Z is reserved for UTC itself — the famous "Zulu time" — with the letters running through the alphabet (skipping J) to cover zones ahead of and behind UTC. It's a separate naming scheme from EST or CET, built for radio communication where a single spoken letter is faster and less error-prone than a full regional name.
08Why abbreviations aren't safe for scheduling
Put the last few sections together and the pattern is clear: the same three letters can point to offsets fourteen hours apart, and even a single, unambiguous abbreviation like EST changes its actual offset twice a year as daylight saving starts and stops. Neither problem is rare — they're built into how these abbreviations work.
When you're scheduling something that anyone outside your own region or time zone will read — a calendar invite, a support ticket, a flight confirmation — skip the abbreviation and write the UTC offset or a full date + time + offset instead. Our guide to converting between time zones without mistakes walks through doing that by hand, and the meeting planner does it automatically for a whole group at once.
Look up any abbreviation instantly
Search the full, current list of time zone abbreviations and their UTC offsets — free, no sign-up.
09Frequently asked questions
What does EST stand for?
EST stands for Eastern Standard Time, UTC−5, used across the eastern United States and Canada. For most of the year it becomes EDT, Eastern Daylight Time, UTC−4.
What does CET stand for?
CET stands for Central European Time, UTC+1, used across most of continental Europe. During the summer months it becomes CEST, Central European Summer Time, UTC+2.
Why does CST mean two different things?
CST is used for both Central Standard Time in North America (UTC−6) and China Standard Time (UTC+8). The two are unrelated and off by fourteen hours, so the abbreviation alone doesn't tell you which one is meant.
What's the difference between a standard and daylight abbreviation?
The middle letter usually flips from S to D — EST to EDT, CST to CDT — to show that daylight saving time is in effect and the offset has moved an hour later. The mechanics of why and when that switch happens are covered in our daylight saving time guide.
Should I use time zone abbreviations for international meetings?
It's safer not to rely on them alone. Because abbreviations like CST and IST are ambiguous and standard/daylight offsets shift twice a year, write the UTC offset or a full ISO 8601 timestamp instead when scheduling across time zones.
