US time zones explained
The 50 states span six time zones, from UTC−5 in the East to UTC−10 in Hawaii — a 5–6 hour spread across the country.
The six zones at a glance
| Zone | Standard time | Daylight time | Largest city |
|---|---|---|---|
| Eastern (ET) | EST, UTC−5 | EDT, UTC−4 | New York |
| Central (CT) | CST, UTC−6 | CDT, UTC−5 | Chicago |
| Mountain (MT) | MST, UTC−7 | MDT, UTC−6 (not in most of Arizona) | Phoenix |
| Pacific (PT) | PST, UTC−8 | PDT, UTC−7 | Los Angeles |
| Alaska (AKT) | AKST, UTC−9 | AKDT, UTC−8 | Anchorage |
| Hawaii (HST) | HST, UTC−10 | Not observed | Honolulu |
When it is noon in New York, it is 11:00 AM in Chicago, 10:00 AM in Denver, 9:00 AM in Los Angeles, 8:00 AM in Anchorage, and 7:00 AM (winter) or 6:00 AM (summer) in Honolulu.
Which states are in which zone
Eastern: Connecticut, Delaware, Georgia, Maine, Maryland, Massachusetts, New Hampshire, New Jersey, New York, North Carolina, Ohio, Pennsylvania, Rhode Island, South Carolina, Vermont, Virginia, West Virginia, and Washington DC — plus most of Florida, Indiana, and Michigan and the eastern parts of Kentucky and Tennessee.
Central: Alabama, Arkansas, Illinois, Iowa, Louisiana, Minnesota, Mississippi, Missouri, Oklahoma, and Wisconsin — plus most of Texas, Kansas, Nebraska, and the Dakotas, western Kentucky and Tennessee, the Florida Panhandle, and a few Indiana and Michigan counties.
Mountain: Colorado, Montana, New Mexico, Utah, and Wyoming in full; Arizona on permanent standard time; southern Idaho; and the western edges of Texas, Kansas, Nebraska, the Dakotas, and Oregon.
Pacific: California, Nevada, and Washington in full, nearly all of Oregon, and Idaho's northern Panhandle.
Alaska: all of Alaska except the Aleutian Islands west of 169°30′ W. Hawaii: all of Hawaii, year-round with no DST.
Why the boundaries zigzag
Standard time zones are a railroad invention. Before 1883, US towns each kept their own solar time — Chicago and St. Louis differed by about 9 minutes — which made timetables nearly impossible. On November 18, 1883, the railroads switched the country to four standard zones, and cities adjusted their clocks to match the nearest railroad standard.
Congress made the system law with the Standard Time Act of 1918, which also handed boundary-setting to the Interstate Commerce Commission. Since 1966 that authority has belonged to the US Department of Transportation, which can move a boundary when a community petitions for it — usually to align local clocks with the trading city its economy depends on.
That is why boundaries follow commerce rather than straight meridians: they bend around metro areas, along county lines and rivers, leaving states like Indiana, Kentucky, Tennessee, Texas, and the Dakotas split between two zones. The result is a line that zigzags hundreds of miles from the 90th or 105th meridian in places.
Frequently asked questions
How many time zones does the US have?
Six across the 50 states: Eastern, Central, Mountain, Pacific, Alaska, and Hawaii. Territories such as Puerto Rico and Guam add more.
What is the biggest time difference inside the US?
Between the East Coast and Hawaii: 5 hours in winter and 6 in summer, since Hawaii skips daylight saving time.
Which states are split between two zones?
Thirteen states are split, including Florida, Indiana, Kentucky, Michigan, Tennessee, Texas, Kansas, Nebraska, North and South Dakota, Idaho, and Oregon. Each state page shows where the line runs.