In this guide
Quick answer: a time zone is a region that shares the same clock time. Each is described by its offset from UTC, the world time standard, and many offsets shift by an hour for daylight saving time.
What is UTC?
Coordinated Universal Time (UTC) is the standard that all time zones are measured against. It does not change with the seasons. A zone described as UTC−5 is five hours behind UTC, and UTC+9 is nine hours ahead.
Common offsets
| Place | Standard time | Daylight saving time |
|---|---|---|
| New York (Eastern) | UTC−5 | UTC−4 |
| Chicago (Central) | UTC−6 | UTC−5 |
| Denver (Mountain) | UTC−7 | UTC−6 |
| Los Angeles (Pacific) | UTC−8 | UTC−7 |
| London | UTC+0 | UTC+1 |
| Paris and Berlin | UTC+1 | UTC+2 |
| India | UTC+5:30 | No daylight saving |
| Tokyo | UTC+9 | No daylight saving |
| Sydney | UTC+10 | UTC+11 |
Sydney is in the southern hemisphere, so its daylight saving period runs roughly from October to April.
Not every offset is a whole hour
India is UTC+5:30 and Nepal is UTC+5:45. Some parts of Australia use half-hour offsets too. This is one reason to use a converter instead of counting hours in your head.
One country, one time zone
China spans a very wide area but uses a single time zone, UTC+8. In contrast, the United States has several time zones on the mainland alone, plus Alaska, Hawaii and territories.
Why abbreviations are risky
Time zone abbreviations are not unique. "CST" can mean Central Standard Time, China Standard Time or Cuba Standard Time. "IST" can mean India, Ireland or Israel. Use city names such as "Chicago time" or "Berlin time" to avoid mistakes.
Daylight saving changes the gap
Because countries switch on different dates, the gap between two cities can change for a few weeks each year. See our guide to when daylight saving time ends for the dates.
Scheduling across time zones
- Name the city or zone every time you give a time.
- Use calendar invites, which convert automatically for each attendee.
- Check the actual date, since the date can differ between zones. A late evening meeting in New York is already the next day in Tokyo.
- Avoid the weeks when daylight saving dates differ if you can, or double check them.
Convert a time
The time zone converter handles daylight saving automatically for the date you choose.
Try the calculators
- Time Zone Converter: Convert times between cities
- Date Calculator: Add or subtract days from a date
General information only, not professional advice. See our editorial policy.