What this chart shows
This is a quick reference for the time zone abbreviations you run into in emails, calendar invites, flight details, and news — the two-to-four-letter codes like EST, GMT, CET, and IST. Each row gives the abbreviation, its full name, its UTC offset, and the region it belongs to, ordered from the furthest behind UTC to the furthest ahead.
One thing to know up front: these abbreviations are informal and not centrally governed. Several sets of letters are reused for completely different zones — CST alone means US Central, China, and Cuba time. So the chart flags the ambiguous ones, and for anything that actually matters you should lean on the UTC offset or the full zone name rather than the letters. The UTC converter and meeting planner work in offsets for exactly that reason.
How to read it
Four steps — the region column is there to save you from the ambiguous ones.
- Find the abbreviation.Scan the left column for the code you saw. The table runs west to east, from UTC−10:00 down to UTC+13:00.
- Read its full name and offset.The next columns give the zone's name and its UTC offset, like Central European Time, UTC+01:00.
- Check the region.If the letters look familiar from more than one place, the region column confirms which zone you actually have.
- Convert with the offset.Add the offset to go from UTC to local, or subtract to go from local to UTC. Copy, print, or download the chart to keep it handy.
Offsets, standard time, and daylight time
Every zone is defined by its offset from UTC — Coordinated Universal Time, the world's reference clock. A zone that is "three hours ahead" is UTC+03:00; three hours behind is UTC−03:00. That offset is the part that never lies, which is why schedulers and software use it instead of the letters.
Most abbreviations come in pairs: a standard-time code for winter and a daylight-time code for summer, one hour apart. When a region "springs forward," it swaps from the first to the second:
- EST → EDT: UTC−05:00 in winter becomes UTC−04:00 in summer.
- CET → CEST: UTC+01:00 becomes UTC+02:00.
- GMT → BST: the UK moves from UTC+00:00 to UTC+01:00.
So a single region uses different letters at different times of year. The offset in this chart is the fixed value each abbreviation stands for; which one is "in force" depends on the date and on whether that region observes daylight saving at all — many, like most of Asia and Hawaii, do not.
IST — India UTC+05:30 · Irish UTC+01:00 · Israel UTC+02:00
BST — British Summer UTC+01:00 · Bangladesh UTC+06:00
AST — Atlantic UTC−04:00 · Arabia UTC+03:00
Quick conversion examples
Reading an abbreviated time and turning it into UTC.
| Local time | Zone | In UTC |
|---|---|---|
| 3:00 PM EST | UTC−05:00 | 20:00 UTC |
| 9:00 AM PST | UTC−08:00 | 17:00 UTC |
| 12:00 PM CET | UTC+01:00 | 11:00 UTC |
| 6:30 PM IST | UTC+05:30 | 13:00 UTC |
| 10:00 AM JST | UTC+09:00 | 01:00 UTC |
To convert a whole time between two named zones without doing the offset math yourself, use the UTC converter or the GMT converter; to find a slot that works across several zones at once, the meeting planner lines them up.
Who uses it, and when
- Remote teams & freelancers decoding a "let's meet at 4 PM CET" from a colleague or client abroad.
- Travellers reading flight times, hotel check-ins, or event schedules quoted in a local abbreviation.
- Developers & sysadmins reading log timestamps and cron schedules, where the safe move is always to normalise to UTC.
- Anyone watching a live broadcast, launch, or sale announced in a zone that isn't theirs.
Working in 24-hour time as you convert? The 24-hour clock chart and military time chart cover the clock side, and the charts hub holds the full reference set.
Frequently asked questions
What is the difference between UTC and GMT?
In everyday use they name the same clock time — both sit at UTC+00:00. The difference is technical: UTC (Coordinated Universal Time) is the modern atomic-clock time standard the world synchronises to, while GMT (Greenwich Mean Time) is the older astronomical time at the Greenwich meridian. For scheduling they are interchangeable; for precise standards work, UTC is the correct reference.
Why do some abbreviations mean more than one time zone?
Abbreviations are informal and not centrally controlled, so the same letters were adopted in different places. CST is US Central Time (UTC−06:00) but also China Standard Time (UTC+08:00) and Cuba Standard Time (UTC−05:00). IST is India (UTC+05:30), Irish (UTC+01:00) or Israel (UTC+02:00). Always confirm the region, and for anything that matters, use the UTC offset or the full IANA zone name.
What is the difference between EST and EDT?
EST is Eastern Standard Time (UTC−05:00), used in winter. EDT is Eastern Daylight Time (UTC−04:00), used in summer when daylight saving is in effect. The clock in that region shifts one hour forward in spring and back in autumn, switching between the two. Every -ST / -DT pair in North America works the same way.
Is Z or Zulu the same as UTC?
Yes. In aviation and the military the letter Z, spoken "Zulu", marks UTC+00:00 — so 1300Z is 13:00 UTC. It is the same instant as GMT in ordinary use. The military time chart shows how those times are written and read.
How do I convert a time from an abbreviation to UTC?
Subtract the zone's offset. If it is 3:00 PM EST and EST is UTC−05:00, then UTC is 3:00 PM + 5 hours = 8:00 PM, i.e. 20:00 UTC. For a UTC+ zone you subtract too: 9:00 AM CET (UTC+01:00) is 8:00 AM UTC. Our UTC converter does this both ways instantly.
Are these abbreviations official?
Mostly no. They are common usage rather than a formal standard, and because several are ambiguous they should not be relied on for scheduling. The authoritative reference is the IANA Time Zone Database, which identifies zones by region name — like America/New_York or Europe/Paris — and tracks their exact offsets and daylight rules.
Does IST mean India or Ireland?
Most often India Standard Time (UTC+05:30). But IST is also Irish Standard Time (UTC+01:00, summer) and Israel Standard Time (UTC+02:00). This chart lists the India meaning as the common default and flags IST as ambiguous — confirm the region before you use it.
Accuracy & sources
Each row pairs an abbreviation with the full name and the fixed UTC offset it denotes, ordered by offset from UTC−10:00 to UTC+13:00. Every offset was checked by hand, and the abbreviations that are reused for more than one zone are flagged in the table and listed in the note above — because these codes are informal, the honest guidance is to confirm the region and rely on the offset.
Zone offsets and daylight-saving rules are maintained by the IANA Time Zone Database, the authoritative source used by operating systems and programming languages worldwide, which identifies zones by region name (such as America/New_York) rather than by these abbreviations. Written and reviewed by Fletcher Langley, and re-checked whenever the chart changes — last reviewed August 2026.
About the author
Operations and workforce-systems specialist with 14+ years inside shift-based industries and payroll platforms, and a BS in Industrial Engineering. Fletcher writes and reviews the calculators, converters, and guides here — from overnight-shift math to decimal payroll hours — drawing on years spent translating between 12-hour, 24-hour, and military time for real timesheets.
Written & reviewed by Fletcher Langley · Last updated: August 2026