US Time Zones Explained: The Nine Zones, Who Sets Them and Where the Lines Run

Federal law divides the United States into nine time zones: 15 U.S.C. 261 sets their standard times from Coordinated Universal Time (UTC) retarded by 4 hours (Atlantic) to UTC advanced by 10 hours (Chamorro). The zones are named in 15 U.S.C. 263, and their limits are defined by an order of the Secretary of Transportation, printed in 49 Code of Federal Regulations (CFR) Part 71. Below: a table of all nine zones with the time in each when it is noon in the Eastern zone, the 13 states whose zone lines run inside them, and a one-page card to print.

How many time zones does the US have?

Nine, by statute. The United States Code (U.S.C.) says that “for the purpose of establishing the standard time of the United States, the territory of the United States shall be divided into nine zones.” The law numbers them, and the number of each zone is its offset from UTC: the first zone is UTC “retarded by 4 hours,” the second 5, the third 6, the fourth 7, the fifth 8, the sixth 9, the seventh 10 and the eighth 11. The ninth is the only one ahead of UTC: “Coordinated Universal Time advanced by 10 hours.”

Section 263 gives the names in the same order: Atlantic, eastern, central, mountain, Pacific, Alaska, Hawaii-Aleutian, Samoa and, for the ninth, “known as Chamorro standard time.”

The nine US time zones in one table

The first four columns come from 15 U.S.C. 261 and 263 and from 49 CFR Part 71. The last two are our arithmetic: the daylight saving time (DST) column adds the one hour that 15 U.S.C. 260a(a) says standard time “shall be advanced,” and the noon column counts the hours from the Eastern zone’s standard time of UTC-5.

Zone (law’s number)	Standard time	Offset from UTC	During DST, where observed	When it is 12 noon in the Eastern zone, standard time	Places
1 Atlantic	Atlantic standard time	UTC-4	UTC-3	1 p.m.	Puerto Rico (49 CFR 71.3), U.S. Virgin Islands
2 Eastern	Eastern standard time	UTC-5	UTC-4	12 noon	East of the line in 71.5, and all of Maine (71.4)
3 Central	Central standard time	UTC-6	UTC-5	11 a.m.	Between the lines in 71.5 and 71.7 (71.6)
4 Mountain	Mountain standard time	UTC-7	UTC-6	10 a.m.	Between the lines in 71.7 and 71.9 (71.8)
5 Pacific	Pacific standard time	UTC-8	UTC-7	9 a.m.	West of the line in 71.9, in the continental United States, but no part of Alaska (71.10)
6 Alaska	Alaska standard time	UTC-9	UTC-8	8 a.m.	The entire State of Alaska except the Aleutian Islands west of 169 degrees 30 minutes west longitude (71.11)
7 Hawaii-Aleutian	Hawaii-Aleutian standard time	UTC-10	UTC-9	7 a.m.	All of Hawaii and the western Aleutian Islands (71.12)
8 Samoa	Samoa standard time	UTC-11	UTC-10	6 a.m.	The area between 169 degrees 30 minutes and 172 degrees 30 minutes west longitude, which includes American Samoa (71.13)
9 Chamorro	Chamorro standard time	UTC+10	UTC+11	3 a.m. the next day	Guam and the Northern Mariana Islands (71.14)

The noon column is for standard time. If one place advances its clocks and another stays on standard time, the gap between them changes by an hour.

Who sets US time zones, and who enforces them?

Two branches share the job. Congress fixes the number of zones and their offsets in 15 U.S.C. 261. The same section hands the map to the executive branch: “The limits of each zone shall be defined by an order of the Secretary of Transportation, having regard for the convenience of commerce and the existing junction points and division points of common carriers engaged in interstate or foreign commerce.” That order is 49 CFR Part 71. Its history notes cite amendments through 78 Federal Register (FR) 15884, dated March 13, 2013.

The Uniform Time Act of 1966 adds a mandate, in 15 U.S.C. 260: the Secretary of Transportation is directed to “promote widespread and uniform adoption and observance of the same standard of time within and throughout each such standard time zone.” The Department of Transportation (DOT) website was not readable by our tools, so this story does not describe how a zone change is requested; only the statute and the regulation text are quoted.

Which states are split between time zones?

Part 71 describes each boundary as a path: county lines, rivers, state lines and in one case a city line. The table lists the states where that text follows a line inside the state, with the section and what it names. Several other states border a zone line only along their edges, such as Georgia and Alabama in section 71.5(e).

State	Section	Boundary	What the text names
Michigan	71.5(a)	Eastern and central	The state’s western boundary, and the lines of Gogebic, Ontonagon, Iron, Dickinson and Menominee counties
Indiana	71.5(b)	Eastern and central	County lines, including LaPorte, Starke, Marshall, Pulaski, Jasper, Newton, Gibson, Pike, Warrick, Spencer and Perry
Kentucky	71.5(c)	Eastern and central	County lines, among them Meade, Hardin, Larue, Taylor, Casey, Pulaski and Wayne
Tennessee	71.5(d)	Eastern and central	The lines of Scott, Morgan, Roane, Rhea and Hamilton counties
Florida	71.5(f)	Eastern and central	“along the middle of the main channel of the Apalachicola River,” then the Jackson River, the Intracoastal Waterway and the west line of Gulf County
North Dakota	71.7(a)	Central and mountain	The Missouri, Yellowstone and Little Missouri rivers and lines in Mercer, Morton and Sioux counties
South Dakota	71.7(b)	Central and mountain	The Missouri River near Pierre and the lines of Jones, Mellette and Todd counties
Nebraska	71.7(c)	Central and mountain	The South Dakota-Nebraska boundary, section and range lines and county lines
Kansas	71.7(d)	Central and mountain	The Kansas-Colorado boundary and the lines of Sherman, Logan, Wallace, Wichita, Greeley and Hamilton counties
Texas	71.7(e)	Central and mountain	“the east line of Hudspeth County, Tex.” down to the Mexican border
Idaho	71.9(a)	Mountain and Pacific	“westerly along the main channel of the Salmon River to the Idaho-Oregon boundary”
Oregon	71.9(a)	Mountain and Pacific	The north and west lines of Malheur County
Nevada	71.9(b)	Mountain and Pacific	The boundaries of the City of West Wendover

Section 71.5(h) puts all municipalities on the eastern and central line in the central zone. Sections 71.7(g) and 71.9(d) put those on the other two lines in the mountain zone, with one exception in 71.7(g): Murdo, South Dakota, is in the central zone. Alaska has two zones as well, because Part 71 puts the Aleutian Islands west of 169 degrees 30 minutes west longitude in Hawaii-Aleutian.

Do all US time zones change their clocks?

The law sets the default. During the period “commencing at 2 o’clock antemeridian on the second Sunday of March” and “ending at 2 o’clock antemeridian on the first Sunday of November,” each zone’s standard time is advanced one hour (15 U.S.C. 260a(a)). The law allows two exemptions: a state that lies entirely within one zone “may by law exempt itself,” provided the whole state keeps standard time, and a state with parts in more than one zone may exempt either the entire state or “the entire area of the State lying within any time zone.” This story does not list which states have exempted themselves, because no official list was confirmed.

The National Institute of Standards and Technology (NIST) says at time.gov that “the change to Standard Time occurs at 2 a.m. (local time) on Sunday 11/01/2026.” Under the rule in 260a, the next advance falls on Sunday, March 14, 2027, and the next return to standard time on Sunday, Nov. 7, 2027; those two dates are our computation from the statute, not a published DOT notice. Our daylight saving time page tracks the date, and the 2027 clock changes story covers it in detail. The November 1 change is already past.

Print the nine-zone card

The one-page US Time Zones Card, linked below this story, lists the nine zones in the law’s order with their UTC offsets, the three boundary sections of Part 71 and four rules quoted from the statutes. Pair it with a 2027 printable yearly calendar to mark the March 14 and Nov. 7, 2027 changes. For how the zones line up at the turn of the year, see the midnight countdown for every time zone.