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Major World Time Zones — Quick Reference
The table below lists the most widely used time zones worldwide with their standard abbreviation and UTC offset. Regions with DST show both standard and daylight abbreviations (e.g., EST/EDT).
| Abbreviation | UTC Offset | Region |
|---|---|---|
| EST/EDT | UTC−5/−4 | Eastern USA & Canada |
| CST/CDT | UTC−6/−5 | Central USA & Canada |
| MST/MDT | UTC−7/−6 | Mountain USA & Canada |
| PST/PDT | UTC−8/−7 | Pacific USA & Canada |
| BRT | UTC−3 | Brazil |
| GMT/BST | UTC+0/+1 | United Kingdom |
| CET/CEST | UTC+1/+2 | Central Europe |
| MSK | UTC+3 | Russia (Moscow) |
| GST | UTC+4 | UAE & Gulf |
| IST | UTC+5:30 | India |
| BST | UTC+6 | Bangladesh |
| ICT | UTC+7 | Southeast Asia |
| CST | UTC+8 | China, Singapore, HK |
| JST | UTC+9 | Japan & Korea |
| AEST/AEDT | UTC+10/+11 | Eastern Australia |
| NZST/NZDT | UTC+12/+13 | New Zealand |
Source: IANA timezone database. Offsets shown reflect standard and DST values where applicable.
Understanding World Clocks and Time Zones
A world clock shows the current local time in multiple cities simultaneously. Unlike a single clock that can only display one time, a world clock lets you compare times across countries, plan international calls, and track business hours in other regions — all at a glance. Each city's time is determined by its time zone, which is a political and geographic region that shares the same UTC offset. Some large countries, like the United States, Russia, and Australia, span multiple time zones; others, like China and India, use a single zone nationwide despite their geographic breadth.
All times are anchored to UTC (Coordinated Universal Time), the global reference point. A city’s local time equals UTC plus its current offset. The offset can change twice a year in regions that observe daylight saving time (DST), which is why checking live times is more reliable than memorizing fixed offsets.
The IANA timezone database (also called the Olson database) is the definitive source of timezone rules. It is maintained collaboratively and updated whenever a government changes its timezone rules. Every major operating system — Windows, macOS, Linux, iOS, Android — ships with IANA data, and so does every modern web browser. TimeandTool uses the same database via the JavaScript Intl.DateTimeFormat API.
How DST Affects World Clock Readings
Spring Forward
When DST begins, clocks move forward one hour — e.g., 2:00 AM becomes 3:00 AM. This means one fewer hour of sleep on that night, and sunrise/sunset both shift one hour later by the clock.
Fall Back
When DST ends, clocks move back one hour — 2:00 AM becomes 1:00 AM again. This creates an ambiguous hour that occurs twice, which is why timezone-aware timestamps are essential for scheduling.
Transition Gaps Between Countries
Different countries switch DST on different dates. The US changes in mid-March; the EU follows two weeks later. During this gap, the time difference between, say, New York and London shifts by one hour — a common source of missed meetings.
Countries Without DST
Most of Asia, Africa, and South America do not observe DST. Countries near the equator (where daylight varies little year-round) see no benefit in shifting clocks. Japan, China, India, and the majority of African nations maintain a fixed UTC offset throughout the year.