World Time Zones & Daylight Saving Time Guide

What Is a Time Zone?

A time zone is a region of the world that observes a uniform standard time for legal, commercial, and social purposes. Because the Earth rotates 360 degrees in 24 hours, it is divided into roughly 24 longitudinal bands, each about 15 degrees wide, corresponding to one hour of time difference.

The global reference point is UTC (Coordinated Universal Time), which replaced the older Greenwich Mean Time (GMT) as the standard. All time zones are described by their offset from UTC, such as UTC+8 or UTC-5.

Major World Time Zones

Here are the UTC offsets for major cities and regions worldwide. Use this table to work out the time difference between two places.

UTC Offset	Major Cities / Regions
UTC-10	Honolulu, Hawaii
UTC-8	Los Angeles, San Francisco, Vancouver, Seattle
UTC-7	Denver, Phoenix (Arizona has no DST)
UTC-6	Chicago, Mexico City, Dallas
UTC-5	New York, Toronto, Miami, Boston
UTC-4	Caracas, Santiago
UTC-3	Buenos Aires, São Paulo
UTC 0	London, Dublin, Lisbon, Accra
UTC+1	Paris, Berlin, Madrid, Rome, Amsterdam
UTC+2	Athens, Cairo, Johannesburg, Helsinki
UTC+3	Moscow, Nairobi, Istanbul, Riyadh
UTC+4	Dubai, Abu Dhabi, Baku
UTC+5	Karachi, Islamabad, Tashkent
UTC+5:30	Mumbai, New Delhi, Colombo
UTC+7	Bangkok, Jakarta, Hanoi
UTC+8	Beijing, Shanghai, Singapore, Hong Kong, Manila, Perth
UTC+9	Tokyo, Seoul, Osaka
UTC+9:30	Adelaide, Darwin
UTC+10	Sydney, Melbourne, Brisbane
UTC+12	Auckland, Wellington, Fiji

Note: The table shows standard time. Many regions shift +1 hour during Daylight Saving Time in summer.

How to Calculate Time Differences

To find the time difference between two places, simply subtract their UTC offsets. For example:

London is UTC 0 and New York is UTC-5, so New York is 5 hours behind London.
Tokyo is UTC+9 and Sydney is UTC+10, so Sydney is 1 hour ahead of Tokyo.
New York is UTC-5 and Beijing is UTC+8, so Beijing is 13 hours ahead of New York.

Remember: if the difference crosses the date line, the date may change too. When it is noon on Tuesday in New York, it is already 1 AM on Wednesday in Beijing.

Daylight Saving Time (DST)

Daylight Saving Time is the practice of setting clocks forward by one hour during the warmer months to extend evening daylight. Clocks "spring forward" in spring and "fall back" in autumn.

Key DST Facts

When: Most Northern Hemisphere countries observe DST from about March to November; Southern Hemisphere countries from about October to April.
Who observes it: Most of the United States, Canada, Europe, Australia, and New Zealand. Much of Asia and Africa do not use DST.
Who does not: Japan, India, China, and most of Africa do not observe DST at all.
Exceptions within countries: Arizona and Hawaii in the US do not observe DST, and the state of Queensland in Australia does not.

Travel tip: Always double-check DST dates before travelling or scheduling international calls — they vary by country and can shift the time difference by an hour.

Time Zone Curiosities

China uses a single time zone (UTC+8) despite spanning five geographic time zones, so the far west sees sunrise very late.
India and Sri Lanka use 30-minute offsets (UTC+5:30), as do Iran and Afghanistan.
Nepal uses UTC+5:45, one of the only 45-minute offsets in the world.
The International Date Line zigzags around island nations to keep each country on a single date.

Frequently Asked Questions

What's the difference between UTC and GMT?

GMT (Greenwich Mean Time) is a time zone based on the line of longitude through Greenwich, London. UTC (Coordinated Universal Time) is a more precise scientific standard. For everyday purposes, they are effectively the same.

Why is the time difference sometimes 30 or 45 minutes?

Some countries choose offsets that are not whole hours to align daylight more closely with their geographic position or for historical reasons. India's 30-minute offset is a well-known example.

Does the whole world change clocks for DST at the same time?

No. Different countries start and end DST on different dates. Europe, the US, and the Southern Hemisphere all shift at different times, which is why the time difference between cities can change throughout the year.

What does "Zulu time" mean?

Zulu time is military and aviation terminology for UTC. The letter "Z" (Zulu) denotes UTC in time zone designations, widely used in aviation, shipping, and the military.