Timezone reference
Timezone Abbreviations & IANA Zones
A reference guide for common timezone abbreviations UTC, GMT, EST, BST, CET, PST, JST and more with offsets, DST notes, and example cities. For exact scheduling, always use a city name or IANA identifier rather than a short abbreviation.
Common abbreviations
UTC
Coordinated Universal Time
The global time standard used for technical systems, aviation, and international coordination. Never changes for DST.
GMT
Greenwich Mean Time
Closely associated with London in winter. GMT itself does not shift, but UK local time moves to BST during summer.
EST
Eastern Standard Time
Used in eastern North America during standard time (autumn/winter). Switches to EDT in spring.
EDT
Eastern Daylight Time
The daylight saving counterpart to EST, active in eastern North America during spring and summer.
BST
British Summer Time
UK daylight saving time, active from late March to late October. Standard UK time is GMT (UTC+00:00).
CET
Central European Time
Standard time for much of Central Europe in autumn and winter. Most CET locations switch to CEST in summer.
CEST
Central European Summer Time
Daylight saving time for Central Europe, active from late March to late October.
PST
Pacific Standard Time
Used on the US and Canadian Pacific coast during standard time (autumn/winter). Switches to PDT in spring.
JST
Japan Standard Time
Used throughout Japan year-round. Japan does not observe daylight saving time, making JST a stable reference.
AEST
Australian Eastern Standard Time
Standard time for eastern Australia. Sydney and Melbourne switch to AEDT in summer; Brisbane stays on AEST year-round.
Why abbreviations can mislead
Use city names for exact scheduling
Timezone abbreviations are convenient shorthand, but they are not globally unique. CST can mean Central Standard Time (UTC−06:00 in North America), China Standard Time (UTC+08:00), or Cuba Standard Time (UTC−05:00). IST can mean India Standard Time, Irish Standard Time, or Israel Standard Time three different offsets.
For recurring meetings, calendar invites, and automated systems, always use a city name or the full IANA identifier (e.g. America/Chicago) so the correct DST rules are applied automatically.
Ambiguous abbreviations
CST
Central Standard (UTC−6), China Standard (UTC+8), Cuba Standard (UTC−5)
IST
India Standard (UTC+5:30), Irish Standard (UTC+1), Israel Standard (UTC+2)
AST
Atlantic Standard (UTC−4), Arabia Standard (UTC+3), Alaska Standard (UTC−9)
BST
British Summer (UTC+1), Bangladesh Standard (UTC+6)
PST
Pacific Standard (UTC−8), Philippine Standard (UTC+8)
IANA timezone identifiers
All zones in the Timezzon city database
These are the IANA timezone identifiers used by cities in Timezzon. Each identifier encodes the full history of DST rules and offset changes for that location. Use these in code, calendar systems, and APIs for reliable date-aware time handling.
Common questions
What is the difference between UTC and GMT?
UTC (Coordinated Universal Time) is the modern international time standard maintained by atomic clocks. GMT (Greenwich Mean Time) is a historical timezone associated with the Greenwich meridian. For most practical purposes they show the same time, but UTC is the precise technical standard. The UK uses GMT in winter and BST (UTC+01:00) in summer.
Why do timezone abbreviations sometimes cause confusion?
Many abbreviations are not globally unique. For example, CST can mean Central Standard Time (UTC−06:00 in North America), China Standard Time (UTC+08:00), or Cuba Standard Time (UTC−05:00). For exact scheduling, always use a city name or the full IANA timezone identifier (e.g. America/New_York) rather than a short abbreviation.
What is an IANA timezone?
The IANA timezone database (also called the tz database or Olson database) is the authoritative global list of timezone rules. Each entry is identified by a region/city name such as Europe/London or America/New_York. These identifiers encode all historical and current DST rules for that location, making them far more reliable than abbreviations for date-aware calculations.
How does Daylight Saving Time affect timezone offsets?
When a location observes DST, its UTC offset shifts typically by one hour. For example, New York moves from EST (UTC−05:00) to EDT (UTC−04:00) in spring. Not all countries observe DST, and those that do may change clocks on different dates. This means the time difference between two cities can change by an hour or two at certain points in the year.
Which countries do not observe Daylight Saving Time?
Many countries near the equator do not observe DST because seasonal daylight variation is minimal. These include Japan, China, India, most of Africa, Singapore, and the UAE. Some countries that previously observed DST have abolished it in recent years.