September 16, 2026 8 min read

Time Zone Abbreviations: A Full List and the Ones That Clash

A time zone abbreviation such as EST, CET or IST is a short label for a zone's standard or summer time. EST is Eastern Standard Time, UTC-5; CET is Central European Time, UTC+1. The labels are convenient but not standardized, and several of them stand for two or three zones hours apart. Below are the common abbreviations by region with their offsets, the clashes to watch, and what to write instead.

Why abbreviations are risky

No international body assigns time zone abbreviations. They grew out of local habit, and the same three letters were picked independently in different countries. The IANA time zone database, which supplies the time rules inside most operating systems and phones, uses abbreviations only as display labels. Its documentation warns that they "are ambiguous in practice: e.g., CST means one thing in China and something else in North America, and IST can refer to time in India, Ireland or Israel," and advises using numeric offsets such as -0600 instead.

The database also refuses to invent labels. Its rule is to use abbreviations "in common use among English-speakers", and where none exists it shows the bare offset. That is why a computer set to Dubai shows "+04" rather than GST, and Istanbul shows "+03" rather than TRT. Phones and browsers often display longer names such as "Pacific Time", which come from a separate Unicode project, CLDR, that groups zones into named "metazones".

Two habits cause most mistakes. People write the standard-time label all year ("EST" in July, when New York is actually on EDT, UTC-4), and people assume a label means their own region's version. Every abbreviation below links to its page on this site, and the list of time zones shows all of them with the current time.

North America

In the United States and Canada, standard-time labels end in S and summer labels in D, for "daylight". Spoken and generic forms drop the middle letter: ET, CT, MT and PT mean "whichever is in force", which is the safest way to write a recurring time.

Western Canada is changing labels. British Columbia and Alberta have ended seasonal clock changes, and in the tz database Vancouver shows MST (UTC-7) and Edmonton shows CST (UTC-6) all year from November 1, 2026. Local news calls the same thing "permanent daylight time", which describes the clock rather than the label. The background is in our post on Canada's clock change.

South of the United States, two labels you will meet are ART, Argentina Time, and BRT, Brasília Time, both UTC-3 with no daylight saving time.

Europe and Africa

Ireland is the odd one. Under Irish law the summer offset, UTC+1, is the country's standard time and winter time is the exception, so Dublin's summer label is IST (Irish Standard Time), not a "daylight" label. In the European Union and the UK, the summer switch happens on the last Sunday of March and the switch back on the last Sunday of October, both at 01:00 UTC, so London, Paris and Athens change labels at the same instant.

Asia and Oceania

Southern hemisphere summer labels run the opposite way round the calendar: Sydney is on AEDT from early October to early April, so a "Sydney 9:00" meeting in January is UTC+11. The database only uses letters where English speakers commonly do, so Bangkok, Singapore, Kuala Lumpur, Kathmandu and Tehran appear in software as +07, +08, +0545 and +0330. One more quirk from the IANA list: it gives Manila "PST" for Philippine Standard Time, the same letters as Pacific Standard Time in Los Angeles, 16 hours away.

Abbreviations with more than one meaning

These are the clashes that cause missed calls. The gap column shows how far apart the readings are in hours, so you can see what a wrong guess costs.

Context usually settles it, but not always. "Webinar at 10:00 CST" from a company with offices in Chicago and Shanghai is a coin toss between two times 14 hours apart (13 in the American summer). An airline email from Israel that says "IST" means UTC+2 in winter, while a recruiter in Bengaluru means UTC+5:30. Each clash has a page that shows all its meanings with the live time, such as what IST can mean and what CST can mean.

Use UTC offsets or IANA names instead

For anything that matters, write the offset or the place. "15:00 UTC" or "15:00 (UTC-5)" cannot be misread, and naming a city ("10:00 Chicago time") lets the reader's calendar work out the rest. Software uses IANA zone names such as America/Chicago, Asia/Kolkata or Europe/Dublin, which identify a place's whole history of offsets, including future daylight saving changes. That is why a calendar invite created with a zone name stays correct after a clock change, while one typed as "EST" may not. The database itself is covered in our post on the IANA time zone database, and the house style we recommend is in how to write times across time zones.

If you must use letters, use the generic form for recurring events (ET, PT) and the exact form only for a specific date, and never write EST for a July meeting. The difference between the two Eastern labels is explained in EST vs EDT, and the bigger picture is in how time zones work.

When an invite arrives with a label you are not sure about, put the time and the sender's city into our time zone converter before you accept it.

Frequently asked questions