Time Zones in the United States Explained
Country Guides
The United States is wide enough to stretch across the better part of half the planet, so a single national clock was never going to work. Instead the country is split into several time zones — four across the contiguous "lower 48" states, plus more for Alaska, Hawaii and the overseas territories. This guide explains how many there are, how the offsets work, and why a few places never change their clocks.
- The contiguous US has four main time zones: Eastern, Central, Mountain and Pacific.
- Counting Alaska and Hawaii–Aleutian there are six zones used by the states, and nine including the territories.
- Coast to coast there is a 3-hour difference: when it is noon in New York it is 9:00 a.m. in Los Angeles.
- Most of the country observes Daylight Saving Time, but Arizona (except the Navajo Nation) and Hawaii do not.
How Many Time Zones Does the US Have?
The answer depends on what you count. The 48 contiguous states span four time zones. Add Alaska and Hawaii and the 50 states use six. Include the inhabited territories — Puerto Rico, the US Virgin Islands, Guam, the Northern Mariana Islands and American Samoa — and the United States touches nine standard time zones in total, ranging from UTC−11 in American Samoa all the way to UTC+10 in Guam.
Time zone boundaries are not drawn casually. In the US they are defined by federal law and administered by the Department of Transportation, which is also responsible for the rules on Daylight Saving Time.
The Time Zones of the 50 States
These are the six zones used by the states, listed from west to east. Standard time applies in winter; the Daylight Saving column shows the offset from mid-March to early November.
| Time zone | Standard time | During DST | Example cities |
|---|---|---|---|
| Hawaii–Aleutian (HST) | UTC−10:00 | UTC−10:00* | Honolulu |
| Alaska (AKST) | UTC−09:00 | UTC−08:00 | Anchorage, Juneau |
| Pacific (PST) | UTC−08:00 | UTC−07:00 | Los Angeles, Seattle |
| Mountain (MST) | UTC−07:00 | UTC−06:00 | Denver, Phoenix* |
| Central (CST) | UTC−06:00 | UTC−05:00 | Chicago, Houston |
| Eastern (EST) | UTC−05:00 | UTC−04:00 | New York, Washington D.C. |
*Hawaii and most of Arizona (including Phoenix) do not observe Daylight Saving Time, so their offset stays the same all year. The Aleutian Islands portion of the Hawaii–Aleutian zone does observe DST.
The Four Main Time Zones
Most of the US population lives within the four zones that cover the contiguous states. Each is one hour apart from the next, so the country reads like a staircase of clocks:
- Eastern Time (ET) — UTC−5 standard, UTC−4 in summer. The most populous zone, covering the East Coast from Maine to Florida and inland to the Great Lakes. New York, Washington D.C., Atlanta and Miami all keep Eastern Time.
- Central Time (CT) — UTC−6 standard, UTC−5 in summer. Covers the middle of the country, including Chicago, Houston, Dallas and New Orleans.
- Mountain Time (MT) — UTC−7 standard, UTC−6 in summer. Covers the Rocky Mountain states such as Colorado, Utah and most of Arizona. Denver is the best-known Mountain Time city.
- Pacific Time (PT) — UTC−8 standard, UTC−7 in summer. The West Coast zone: Los Angeles, San Francisco, Seattle and Las Vegas.
Because Eastern and Pacific sit three hours apart, a 9:00 a.m. start on the East Coast is only 6:00 a.m. on the West Coast — a gap that shapes everything from television broadcast schedules to nationwide conference calls.
Alaska and Hawaii
The two non-contiguous states each have their own zone. Alaska Time (UTC−9) covers almost the entire state, even though Alaska is geographically wide enough to justify more than one zone; it was consolidated for convenience. Hawaii sits at UTC−10 and, crucially, does not change its clocks, so during the US summer it can be a full six hours behind New York rather than the usual five.
The US Territories
Beyond the 50 states, several inhabited territories add three more zones. None of them observe Daylight Saving Time.
| Time zone | Offset | Territories |
|---|---|---|
| Atlantic (AST) | UTC−04:00 | Puerto Rico, US Virgin Islands |
| Samoa (SST) | UTC−11:00 | American Samoa |
| Chamorro (ChST) | UTC+10:00 | Guam, Northern Mariana Islands |
Guam and the Northern Mariana Islands sit on the other side of the International Date Line from the mainland, which is why their offset is positive (UTC+10) while everywhere else in the US is negative.
Daylight Saving Time in the US
Most of the United States springs forward and falls back each year. Under the current rules (set by the Energy Policy Act of 2005), Daylight Saving Time:
- Begins on the second Sunday in March, when clocks jump forward one hour at 2:00 a.m.
- Ends on the first Sunday in November, when clocks fall back one hour.
When DST is active, the abbreviations change from "standard" to "daylight": EST becomes EDT, PST becomes PDT, and so on. To understand the reasoning behind the clock changes, see What Is Daylight Saving Time?
Which Places Do Not Change Their Clocks?
A handful of places stay on standard time all year, which can trip up travellers and remote workers:
- Hawaii — never observes DST.
- Most of Arizona — stays on Mountain Standard Time year-round. The exception is the Navajo Nation in the northeast of the state, which does observe DST.
- All US territories — Puerto Rico, the US Virgin Islands, Guam, the Northern Mariana Islands and American Samoa.
The practical effect is that the time difference between, say, Phoenix and Los Angeles changes with the seasons: they share a clock in winter, but in summer Phoenix is an hour ahead because California has moved its clocks and Arizona has not.
Reading US Time Zone Abbreviations
American time zones are usually written as three-letter codes. The middle letter tells you whether Daylight Saving Time is in effect:
- EST / EDT — Eastern Standard / Daylight Time
- CST / CDT — Central Standard / Daylight Time
- MST / MDT — Mountain Standard / Daylight Time
- PST / PDT — Pacific Standard / Daylight Time
To see which offset a US city is on right now — standard or daylight — open its city page on this site; the current UTC offset is shown next to the clock.
Frequently Asked Questions
How many time zones are in the United States?
The 48 contiguous states use four (Eastern, Central, Mountain, Pacific). All 50 states use six once Alaska and Hawaii–Aleutian are added, and including the territories the US spans nine time zones in total.
What is the time difference between the East and West Coast?
Three hours. Eastern Time is three hours ahead of Pacific Time, so noon in New York is 9:00 a.m. in Los Angeles.
Why does Arizona not change its clocks?
Arizona opted out of Daylight Saving Time decades ago, largely because its intense summer heat makes an extra hour of evening daylight undesirable. The Navajo Nation within Arizona is the one exception and does observe DST.
Is Hawaii always behind the mainland?
Yes, and the gap widens in summer. Because Hawaii does not observe DST, it falls two to three hours behind Pacific Time depending on the season, and up to six hours behind Eastern Time. For the bigger picture, read How Time Zones Work Around the World.