World Time Zones Explained
5 min read
There are 24 primary time zones spanning the globe, but the reality is far messier โ some zones are offset by 30 or 45 minutes, and daylight saving makes it all shift twice a year. Here is how it all works.
The Basics: UTC
UTC = Coordinated Universal Time (the global reference)
All time zones are defined as offsets from UTC (e.g., UTC+5:30)
UTC replaced GMT (Greenwich Mean Time) as the international standard. They refer to the same time, but UTC is more precisely defined using atomic clocks.
Major Time Zones
| Zone | UTC Offset | Major Cities |
|---|---|---|
| PST/PDT | -8/-7 | Los Angeles, Vancouver |
| EST/EDT | -5/-4 | New York, Toronto |
| GMT/BST | 0/+1 | London, Dublin |
| CET/CEST | +1/+2 | Paris, Berlin |
| IST | +5:30 | Mumbai, Delhi |
| CST (China) | +8 | Beijing, Shanghai |
| JST | +9 | Tokyo, Seoul |
| AEST/AEDT | +10/+11 | Sydney, Melbourne |
Daylight Saving Time
About 70 countries observe daylight saving time (DST), shifting clocks forward by one hour in spring and back in autumn:
- โถ Northern hemisphere: Starts March/April, ends October/November
- โถ Southern hemisphere: Starts September/October, ends March/April
- โถ Countries that DON'T observe DST: Japan, China, India, most of Africa, most of Southeast Asia
Time Zone Oddities
- โถ India: One time zone for the entire country (UTC+5:30) despite spanning 2,000+ km east to west
- โถ China: One time zone (UTC+8) for a country wider than the continental US
- โถ Nepal: UTC+5:45 โ one of only a few countries with a 45-minute offset
- โถ Kiribati: UTC+14 โ the first place to ring in each new year
Tips for Working Across Time Zones
- โถ Always specify the time zone when scheduling ("3 PM EST" not just "3 PM")
- โถ Use UTC for coordination โ it never changes with DST
- โถ World clock apps let you see multiple zones at a glance
- โถ Calendar apps automatically convert times when you specify a zone
๐ Try our free time zone tools
Open Tool โ