Time Zone Calculator

Choose a date, a time and the zone it is in, then the zone you want to convert to. The calculator uses the time zone database built into your browser, the same IANA data that phones and computers use, so daylight saving time is applied according to each place's rules on the date you pick. That matters because regions change their clocks on different dates: for a few weeks each spring and fall, the gap between New York and London is four hours instead of five.

What is Time Zone

A time zone is a region that keeps the same standard time. Because the Earth turns 15 degrees of longitude every hour, noon arrives at different moments around the globe, and until the late 19th century most towns kept their own local solar time. That worked when travel was slow, but railways needed shared timetables. In 1883 the US and Canadian railroads adopted standard time zones, and in 1884 the International Meridian Conference in Washington chose the meridian through Greenwich, England, as the prime meridian for longitude and the starting point for world time.

Today, zones are defined as offsets from Coordinated Universal Time (UTC), the atomic-clock based successor to Greenwich Mean Time. In theory each zone spans 15 degrees, but borders follow national and regional boundaries, and governments choose their own offsets. China, which spans about five theoretical zones, uses a single time, UTC+8, while some places use half-hour or 45-minute offsets, such as India (UTC+5:30), Newfoundland (UTC−3:30) and Nepal (UTC+5:45). Offsets run from UTC−12 to UTC+14 on Kiribati's Line Islands, so at some moments three calendar dates are in use at once.

World Time Zone Map

The diagram below arranges common offsets from west to east with example places in each. Moving east, clocks are later; moving west, they are earlier. The International Date Line, roughly along the 180° meridian in the Pacific, is where the calendar date changes: crossing it westward adds a day, and crossing eastward subtracts one. The line zigzags around island nations so that each keeps a single date, which is why Samoa and American Samoa, roughly 80 miles apart, are a full day apart on the calendar.

U.S. Time Zone Map

By federal law, the United States and its territories use nine standard time zones, overseen by the Department of Transportation, which also decides changes to zone boundaries. The contiguous states span four: Eastern, Central, Mountain and Pacific. Alaska has its own zone, while Hawaii and Alaska's western Aleutian Islands share the Hawaii–Aleutian zone. Puerto Rico and the US Virgin Islands are on Atlantic time, American Samoa on Samoa time, and Guam and the Northern Mariana Islands on Chamorro time, ten hours ahead of UTC.

Zone lines do not follow state borders exactly. Parts of Florida, Indiana, Kentucky, Michigan, Tennessee, Kansas, Nebraska, the Dakotas, Texas, Idaho and Oregon are split between two zones, so the local time can change when you cross a county line. Most of Arizona stays on Mountain Standard Time all year, although the Navajo Nation in the northeast of the state does observe daylight saving time.

Daylight Saving Time

Daylight saving time (DST) moves clocks forward one hour in spring and back in autumn, shifting daylight from early morning to evening. It was first adopted widely during World War I to save fuel. In the US, the Energy Policy Act of 2005 set the current schedule, used since 2007. The European Union changes on the same Sundays across its member states, at 01:00 UTC. In the Southern Hemisphere the seasons are reversed, so Australia's and New Zealand's summer time runs from spring in September or October to April. Most countries near the equator, as well as China, India and Japan, do not use DST, and Mexico ended it for most of the country in 2022.

Frequently asked questions