What is the difference between UTC and GMT?

For everyday use they are equivalent. GMT (Greenwich Mean Time) is a time zone, while UTC (Coordinated Universal Time) is a technical time standard. Both show the same time at the Greenwich Meridian.

What does UTC-5 mean?

It means the local time is 5 hours behind UTC. It is the standard offset of the US East Coast (New York, Washington).

How many time zones are there in the world?

There are 24 main time zones, from UTC-12 to UTC+14, but around 38 offsets are actually in use once you count zones with 30- or 45-minute differences, such as India (UTC+5:30).

Does daylight saving time change the difference between cities?

Yes. When a country moves its clock forward by 1 hour in summer, the difference to cities that do not observe daylight saving changes temporarily by 1 hour.

Time zones guide: world time, conversion and examples

This guide explains in plain terms what time zones are, how to read the UTC and GMT labels and how to convert times between cities. Use the quick-reference tables below to answer any question in seconds.

A time zone is a band of the planet that shares the same official time. Earth rotates 360° in 24 hours, so every 15° of longitude is roughly 1 hour apart. The world reference is UTC (Coordinated Universal Time), measured at the Greenwich Meridian.

Quick reference: world time

Standard offset from UTC and the local time when it is 12:00 UTC (noon in Greenwich). Daylight saving time can shift this by 1 hour in regions that observe it.

Quick reference: world time
City	Offset	When it is 12:00 UTC
Los Angeles	UTC-8	04:00
New York	UTC-5	07:00
São Paulo	UTC-3	09:00
London	UTC+0	12:00
Paris	UTC+1	13:00
Dubai	UTC+4	16:00
New Delhi	UTC+5:30	17:30
Shanghai	UTC+8	20:00
Tokyo	UTC+9	21:00
Sydney	UTC+10	22:00

Quick reference: how to convert time zones

To convert a time between two cities, use each one's UTC offset:

Find the UTC offset of the source city and the destination city.
Calculate the difference between the two (destination minus source).
Add that difference to the source time. If it passes 24h it is the next day; if it goes negative it is the previous day.

New York (UTC-5) to London (UTC+0): add 5 hours. 8:00 in New York = 13:00 in London.
London (UTC+0) to Tokyo (UTC+9): add 9 hours. 9:00 in London = 18:00 in Tokyo.
Los Angeles (UTC-8) to New York (UTC-5): add 3 hours. 6:00 in Los Angeles = 9:00 in New York.
New Delhi (UTC+5:30) to London (UTC+0): subtract 5h30. 18:00 in Delhi = 12:30 in London.

Practical examples

Global meeting: scheduling for 14:00 UTC means 9:00 in New York, 14:00 in London, 15:00 in Paris, 18:00 in Dubai and 23:00 in Tokyo.
US East Coast vs. UK: New York is normally 5 hours behind London, shifting by an hour around daylight saving transitions.
Europe vs. India: New Delhi is 4h30 to 5h30 ahead of most of Europe, depending on European summer time.

Quick questions

What is the difference between UTC and GMT?: For everyday use they are equivalent. GMT (Greenwich Mean Time) is a time zone, while UTC (Coordinated Universal Time) is a technical time standard. Both show the same time at the Greenwich Meridian.
What does UTC-5 mean?: It means the local time is 5 hours behind UTC. It is the standard offset of the US East Coast (New York, Washington).
How many time zones are there in the world?: There are 24 main time zones, from UTC-12 to UTC+14, but around 38 offsets are actually in use once you count zones with 30- or 45-minute differences, such as India (UTC+5:30).
Does daylight saving time change the difference between cities?: Yes. When a country moves its clock forward by 1 hour in summer, the difference to cities that do not observe daylight saving changes temporarily by 1 hour.