Time Zones of the USA
Like all time zones worldwide, the time zones for the USA are based on UTC (Coordinated Universal Time, formerly GMT, Greenwich Mean Time - originally based on London, UK).
The United States observes 9 time zones as below:
- four time zones in the contiguous USA
- two time zones beyond the contiguous USA
- three time zones in US territories
The time zone on the east coast is called Eastern Time (ET), divided into:
- Eastern Standard Time (EST), which is used during autumn/winter and is five hours behind UTC
- Eastern Daylight Time (EDT), which is used during spring/summer and is four hours behind UTC
Other US time zones follow the same format; and moving westward, each time zone adds an additional 1-hour offset.
The 4 time zones of the contiguous USA and the 2 timezones (Alaska, Hawaii) beyond the contiguous USA. (Public Domain)
Time zones in the contiguous USA
| zone and abbreviations* |
Standard Time offset from UTC | Daylight Saving Time offset from UTC | states |
| Eastern ET, EST, EDT |
UTC -5:00 | UTC -4:00 | Connecticut, Delaware, District of Columbia, Georgia, Maine, Maryland, Massachusetts, New Hampshire, New Jersey, New York, North Carolina, Ohio, Pennsylvania, Rhode Island, South Carolina, Vermont, Virginia, West Virginia; Partially: Florida, Indiana, Kentucky, Michigan, Tennessee |
| Central CT, CST, CDT |
UTC -6:00 | UTC -5:00 | Alabama, Arkansas, Illinois, Iowa, Louisiana, Minnesota, Mississippi, Missouri, Oklahoma, Wisconsin; Partially: Florida, Indiana, Kansas, Kentucky, Michigan, Nebraska, North Dakota, South Dakota, Tennessee, Texas |
| Mountain MT, MST, MDT |
UTC -7:00 | UTC -6:00 | Arizona, Colorado, Montana, New Mexico, Utah, Wyoming; Partially: Idaho, Kansas, Nebraska, North Dakota, Oregon, South Dakota, Texas |
| Pacific PT, PST, PDT |
UTC -8:00 | UTC -7:00 | California, Nevada, Washington (state); Partially: Idaho, Oregon |
This mnemonic reminds us that in the spring the clocks move forwards and in the autumn (also called "fall" in US English) they move backwards.
Time zones in states beyond the contiguous USA
| zone and abbreviations* | Standard Time offset from UTC | Daylight Saving Time offset from UTC | states |
| Alaskan AKT, AKST, AKDT |
UTC -9:00 | UTC -8:00 | Alaska (excluding western Aleutian Islands) |
| Hawaiian (also called Hawaii-Aleutian) HT, HST, HAST |
UTC -10:00 | UTC -9:00 (observed in western Aleutian Islands only) | Hawaii and western Aleutian Islands in Alaska |
Time zones in US territories
In addition to the six time zones above, the USA observes three time zones in US territories:
- Samoa Time Zone (UTC -11:00) comprising American Samoa in the Pacific
- Chamorro Time Zone (UTC +10:00) comprising Guam and the Norther Mariana Islands in the western Pacific
- Atlantic Time Zone (UTC -4:00) comprising Puerto Rico and the US Virgin Islands in the Caribbean
contiguous (adjective): joined together, touching, adjacent
GMT (abbreviation): Greenwich Mean Time is the standard time in the UK based on the London borough of Greenwich
UTC (abbreviation): Universal Time Coordinated or Coordinated Universal Time, effectively a successor to GMT
*Time zone abbreviations
Typical abbreviations for time zones that may be encountered in the USA:
| ET | Eastern Time |
| EST | Eastern Standard Time |
| EDT | Eastern Daylight Time |
| CT | Central Time |
| CST | Central Standard Time |
| CDT | Central Daylight Time |
| MT | Mountain Time |
| MST | Mountain Standard Time |
| MDT | Mountain Daylight Time |
| PT | Pacific Time |
| PST | Pacific Standard Time |
| PDT | Pacific Daylight Time |
| AKT | Alaska Time |
| AKST | Alaska Standard Time |
| AKDT | Alaska Daylight Time |
| HT | Hawaii Time |
| HST | Hawaii Standard Time |
| HAST | Hawaii-Aleutian Standard Time |