GUIDES · TIME ZONES
EST vs EDT, IST, CET: Time Zone Abbreviations Explained
Quick answer
EST is Eastern Standard Time (UTC−5), used in winter. EDT is Eastern Daylight Time (UTC−4), used from mid-March to early November. If you don't know which applies, write ET (Eastern Time), or better, name a city: “3 pm New York time” is always right. Many abbreviations, including IST, CST, BST and PST, mean different things in different countries.
One letter, one hour, one missed meeting
Time zone abbreviations look precise, but they cause more scheduling mistakes than almost anything else. The most common: writing “EST” in July, when New York is actually on EDT. Anyone who converts “3 pm EST” literally lands an hour off.
The second most common: using an abbreviation that means something else to the reader. To someone in India, IST is India Standard Time. To someone in Dublin or Tel Aviv, it's a different clock entirely. The official time zone database behind most computers and phones warns about exactly this: “these abbreviations are ambiguous in practice” (IANA time zone database).
This guide explains the abbreviations people search for most, which ones clash, and how to write a time that nobody can misread.
EST vs EDT, and the other US pairs
Every mainland US time zone has two names: a standard name for winter and a daylight name for summer. The “S” or “D” in the middle tells you which.
| Zone | Winter (early November to mid-March) | Summer (mid-March to early November) | Written either way |
|---|---|---|---|
| Eastern | EST, UTC−5 | EDT, UTC−4 | ET |
| Central | CST, UTC−6 | CDT, UTC−5 | CT |
| Mountain | MST, UTC−7 | MDT, UTC−6 | MT |
| Pacific | PST, UTC−8 | PDT, UTC−7 | PT |
| Alaska | AKST, UTC−9 | AKDT, UTC−8 | Alaska Time |
| Hawaii | HST, UTC−10 | HST, UTC−10 (no change) | HST (always) |
The US switches to daylight time on the second Sunday in March and back to standard time on the first Sunday in November. Most of Arizona stays on MST all year, so in summer Phoenix matches Los Angeles, not Denver.
Which one should you write? In practice, most people write “EST” all year and mean “whatever time it is in New York.” A careful reader in another country may take it literally. Three safer options:
- ET, CT, MT or PT: correct in every season.
- A city name: “3 pm New York time” can't be misread, even by people who don't know US time zones.
- The correct seasonal name: fine if you're sure of the date. EST is only right between November and March.
Common time zone abbreviations around the world
Here are the abbreviations you're most likely to see in invites and emails, with their offset from UTC. Where a place changes its clocks, both names are listed.
| Abbreviation | Full name | UTC offset | Example city |
|---|---|---|---|
| GMT / BST | Greenwich Mean Time / British Summer Time | +0 / +1 | London |
| CET / CEST | Central European Time / Central European Summer Time | +1 / +2 | Paris, Berlin |
| EET / EEST | Eastern European Time / Eastern European Summer Time | +2 / +3 | Athens |
| MSK | Moscow Time | +3 | Moscow |
| GST | Gulf Standard Time | +4 | Dubai |
| IST | India Standard Time | +5:30 | Mumbai |
| SGT | Singapore Time | +8 | Singapore |
| CST | China Standard Time | +8 | Shanghai |
| PHT / PST | Philippine Time / Philippine Standard Time | +8 | Manila |
| JST | Japan Standard Time | +9 | Tokyo |
| AEST / AEDT | Australian Eastern Standard / Daylight Time | +10 / +11 | Sydney |
| NZST / NZDT | New Zealand Standard / Daylight Time | +12 / +13 | Auckland |
| AST / ADT | Atlantic Standard / Daylight Time | −4 / −3 | Halifax |
| NST / NDT | Newfoundland Standard / Daylight Time | −3:30 / −2:30 | St. John's |
Three things this table shows:
- Europe and Australia change in opposite seasons. When London moves to BST in March, Sydney moves from AEDT back to AEST a week or so later.
- Half-hour and even quarter-hour offsets exist. India is UTC+5:30, Newfoundland UTC−3:30 and Nepal UTC+5:45. Tools that round to whole hours get these wrong.
- Many places never change their clocks. India, China, Japan, Singapore, the Philippines and the UAE keep the same offset all year, so only the other side's change moves the difference.
To check any of these against your own city on a specific date, use a time zone converter.
Abbreviations that mean two (or three) things
These are the ones that cause real mix-ups, because both readings are common and the offsets are far apart.
| Abbreviation | Could mean | Offsets | Gap between readings |
|---|---|---|---|
| IST | India Standard Time · Irish Standard Time · Israel Standard Time | +5:30 · +1 · +2 | Up to 4½ hours |
| CST | Central Standard Time (US) · China Standard Time · Cuba Standard Time | −6 · +8 · −5 | Up to 14 hours |
| BST | British Summer Time · Bangladesh Standard Time | +1 · +6 | 5 hours |
| PST | Pacific Standard Time · Philippine Standard Time | −8 · +8 | 16 hours |
| AST | Atlantic Standard Time · Arabia Standard Time | −4 · +3 | 7 hours |
| GST | Gulf Standard Time · South Georgia Time | +4 · −2 | 6 hours |
Ireland is a special case: under Irish law the summer clock is officially “standard time” and the winter clock is “winter time”, on GMT (Wikipedia). So “IST” in a Dublin email means UTC+1, while the same letters from Bengaluru mean UTC+5:30.
The practical rule: if your team spans countries, never use an abbreviation on its own. The IANA time zone database, which most computers and phones rely on, recommends numeric offsets like “UTC+5:30” instead, for exactly this reason (IANA).
GMT, UTC and Z
For everyday scheduling, GMT and UTC show the same time, but they aren't quite the same thing.
- UTC (Coordinated Universal Time) is the world's reference clock. It never changes for summer, which is why offsets like UTC+8 are written against it.
- GMT (Greenwich Mean Time) is both an older time standard and the name of the UK's winter clock. In summer the UK moves to BST (UTC+1), so “GMT” in a July email from London is usually a mistake for BST.
- Z, as in 14:00Z, means UTC. It comes from military and aviation use (“Zulu time”) and is the standard suffix in date-time formats like 2026-10-27T14:00:00Z.
If you schedule across many countries, UTC is the safest shared reference: “14:00 UTC” means the same moment everywhere, in every season.
How to write a time nobody can misread
Five habits cover almost every case.
- Name a city, not a zone. “Tuesday 3 pm New York time” survives every clock change and every reader. Everyone knows roughly where New York is; far fewer know what CT covers.
- Give both sides' local times. “3 pm New York / 8 pm London” does the conversion for your reader and exposes any mistake straight away.
- Add the date when it changes. “Friday 6 pm New York (Saturday 7 am Manila)” stops people turning up a day early or late.
- Use a UTC offset for technical or legal text. “15:00 UTC−4” or “19:00 UTC” is unambiguous in contracts, release notes and system messages.
- Send a calendar invite. Invites store the exact moment and show it in each person's own time zone, so the abbreviation stops mattering.
When you receive a time with an ambiguous abbreviation, check which city the sender is in, then convert it for the actual date, not today's date. Around the March and November clock changes, the same abbreviation can be an hour off. Our guide to the daylight saving gap weeks explains why.
| Instead of | Write |
|---|---|
| “3 pm EST” (in July) | “3 pm ET” or “3 pm New York time” |
| “Call at 10 IST” | “Call at 10 am Bengaluru time (UTC+5:30)” |
| “Deadline 5 pm CST” | “Deadline 5 pm Chicago time” or “5 pm Shanghai time” |
| “Webinar at 2 pm GMT” (in summer) | “Webinar at 2 pm London time (BST)” |
| “Meet at 9 PST” | “Meet at 9 am Los Angeles time” or “9 am Manila time” |
Frequently asked questions
What is the difference between EST and EDT?
EST (Eastern Standard Time) is UTC−5 and applies from early November to mid-March. EDT (Eastern Daylight Time) is UTC−4 and applies the rest of the year. New York, Toronto and Miami switch between them.
Is it EST or EDT right now?
From the second Sunday in March to the first Sunday in November, the US East Coast is on EDT. The rest of the year it's on EST. If you're unsure, write ET or “New York time”, which is correct all year.
What time zone is IST?
Most often India Standard Time, UTC+5:30. It can also mean Irish Standard Time (UTC+1, Ireland's summer time) or Israel Standard Time (UTC+2). Check where the sender is.
What is the difference between CET and CEST?
CET (Central European Time) is UTC+1, used in winter. CEST (Central European Summer Time) is UTC+2, used from the last Sunday in March to the last Sunday in October in Paris, Berlin, Rome, Madrid and most of the EU.
Is GMT the same as UTC?
For scheduling, yes: they show the same time. But GMT is also the UK's winter clock, and in summer London is on BST, one hour ahead of GMT and UTC.
Does PST mean Pacific or Philippine time?
It can mean either: Pacific Standard Time is UTC−8 and Philippine Standard Time is UTC+8, 16 hours apart. Use a city name when writing to people in either region.
Live clocks and converters
See the time now in EST, PST, IST, GMT, UTC, CET, AEST, with which abbreviation is in effect today. Or convert: EST to IST, PST to IST, IST to EST, CST to IST, EST to PST, PST to EST, EST to PHT, UTC to EST, EST to GMT, EST to CET. All are listed on the time zones page.
Convert any time
The WherOra time converter shows any moment in up to six cities at once, using each city's rules for the date you choose, including daylight saving changes.