United States time zone history

The United States has 29 zones of its own in the tz database, more than any other country. Standard times run from UTC−10 (Adak) to UTC−5 (New York), a spread of 5 hours. 27 of the 29 zones still change clocks for summer time under the current rules; the other 2 do not. The Metlakatla zone has changed standard time most often since 1970: 3 times.

29 zones · 27 with seasonal clock changes under the rules in tzdata 2026f · Convert a time

The 29 zones of the United States since 1970

How to read this chart

Zones at a glance

Zone	Area covered	Standard time	Clock changes today	New standard times since 1970
Detroit	Michigan (most areas)	UTC−5	yes	0
Indianapolis, Indiana	Indiana (most areas)	UTC−5	yes	0
Louisville, Kentucky	Louisville area, Kentucky	UTC−5	yes	2
Marengo, Indiana	Crawford County, Indiana	UTC−5	yes	2
Monticello, Kentucky	Wayne County, Kentucky	UTC−5	yes	1
New York	Eastern time, most areas	UTC−5	yes	0
Petersburg, Indiana	Pike County, Indiana	UTC−5	yes	3
Vevay, Indiana	Switzerland County, Indiana	UTC−5	yes	0
Vincennes, Indiana	Daviess, Dubois, Knox and Martin counties, Indiana	UTC−5	yes	2
Winamac, Indiana	Pulaski County, Indiana	UTC−5	yes	2
Beulah, North Dakota	Mercer County, North Dakota	UTC−6	yes	1
Center, North Dakota	Oliver County, North Dakota	UTC−6	yes	1
Chicago	Central time, most areas	UTC−6	yes	0
Knox, Indiana	Starke County, Indiana	UTC−6	yes	2
Menominee	Michigan counties on the Wisconsin border	UTC−6	yes	1
New Salem, North Dakota	Rural Morton County, North Dakota	UTC−6	yes	1
Tell City, Indiana	Perry County, Indiana	UTC−6	yes	1
Boise	South Idaho and east Oregon	UTC−7	yes	0
Denver	Mountain time, most areas	UTC−7	yes	0
Phoenix	Arizona (most areas)	UTC−7	no	0
Los Angeles	Pacific time	UTC−8	yes	0
Anchorage	Alaska (most areas)	UTC−9	yes	1
Juneau	Juneau area, Alaska	UTC−9	yes	3
Metlakatla	Annette Island, Alaska	UTC−9	yes	3
Nome	West Alaska	UTC−9	yes	1
Sitka	Sitka area, Alaska	UTC−9	yes	1
Yakutat	Yakutat, Alaska	UTC−9	yes	0
Adak	Western Aleutian Islands, Alaska	UTC−10	yes	1
Honolulu	Hawaii	UTC−10	no	0

What sets each zone apart

Detroit: Detroit kept local mean time (UTC−5:32:11) until 1905, the latest switch of the 29 zones in the United States.
New York: Standard time has stayed at UTC−5 since 1883, tied second-longest run among the 148 zones with no change of standard time since 1970.
Petersburg, Indiana: The Petersburg, Indiana zone has changed its standard time 3 times since 1970, tied for the most among the 29 zones in the United States. On standard time, clocks at Petersburg, Indiana run 49 minutes ahead of local mean solar time, the third-largest gap of the 17 zones on UTC−5 standard time whose clocks run ahead of the sun.
Vincennes, Indiana: On standard time, clocks at Vincennes, Indiana run 50 minutes ahead of local mean solar time, the second-largest gap of the 17 zones on UTC−5 standard time whose clocks run ahead of the sun.
Boise: Boise left local mean time (UTC−7:44:49) in 1883, tied for the earliest switch among the 11 zones on UTC−7 standard time with local mean time in the record. Clocks have been changed 114 times since 1970, tied for the most among the 12 zones on UTC−7 standard time.
Denver: Standard time has stayed at UTC−7 since 1883, tied second-longest run among the 148 zones with no change of standard time since 1970. Denver left local mean time (UTC−6:59:56) in 1883, tied for the earliest switch among the 11 zones on UTC−7 standard time with local mean time in the record.
Phoenix: The Phoenix zone has kept UTC−7 since 1883, with no clock changes since 1970, tied second-longest run among the 148 zones with no change of standard time since 1970. Phoenix left local mean time (UTC−7:28:18) in 1883, tied for the earliest switch among the 11 zones on UTC−7 standard time with local mean time in the record.
Los Angeles: Standard time has stayed at UTC−8 since 1883, tied second-longest run among the 148 zones with no change of standard time since 1970.
Anchorage: On standard time, clocks at Anchorage run 1 hour ahead of local mean solar time, the third-largest gap of the 20 zones in the United States whose clocks run ahead of the sun.
Juneau: The Juneau zone has changed its standard time 3 times since 1970, tied for the most among the 29 zones in the United States.
Metlakatla: The Metlakatla zone has changed its standard time 3 times since 1970, tied for the most among the 29 zones in the United States. The latest change of standard time came on January 20, 2019, from UTC−8 to UTC−9.
Nome: On standard time, clocks at Nome run 2 hours 2 minutes ahead of local mean solar time, the third-largest gap of the 233 zones whose clocks run ahead of the sun. The record holds 6 different UTC offsets, the most of the 29 zones in the United States.
Adak: On standard time, clocks at Adak run 1 hour 47 minutes ahead of local mean solar time, the seventh-largest gap of the 233 zones whose clocks run ahead of the sun.

How the zones compare with New York since 1970

Detroit: same time as New York except 616 days in 1970–1972 and 1975.
Louisville, Kentucky: same time as New York except 294 days in 1974.
Monticello, Kentucky: usually 1 hour behind New York; different on 9,562 days in 1970–2026; same time today.
Indianapolis, Indiana: same time as New York except 7,055 days in 1971–2005.
Vincennes, Indiana: same time as New York except 7,635 days in 1971–2007.
Winamac, Indiana: same time as New York except 7,398 days in 1971–2007.
Marengo, Indiana: same time as New York except 6,257 days in 1974 and 1976–2005.
Petersburg, Indiana: same time as New York except 9,025 days in 1970–2007.
Vevay, Indiana: same time as New York except 6,684 days in 1973–2005.
Chicago: usually 1 hour behind New York; different on 5 days in 1970–2026.
Tell City, Indiana: usually 1 hour behind New York; different on 6,187 days in 1970–2026.
Knox, Indiana: usually 1 hour behind New York; different on 2,377 days in 1970–2026.
Menominee: usually 1 hour behind New York; different on 666 days in 1970–2026.
Center, North Dakota: usually 1 hour behind New York; different on 8,334 days in 1970–2026.
New Salem, North Dakota: usually 2 hours behind New York; different on 8,472 days in 1970–2026; 1 hour behind today.
Beulah, North Dakota: usually 2 hours behind New York; different on 5,905 days in 1970–2026; 1 hour behind today.
Denver: usually 2 hours behind New York; different on 10 days in 1970–2026.
Boise: usually 2 hours behind New York; different on 38 days in 1970–2026.
Phoenix: usually 3 hours behind New York; different on 8,613 days in 1970–2026; 2 hours behind today.
Los Angeles: usually 3 hours behind New York; different on 14 days in 1970–2026.
Anchorage: usually 4 hours behind New York; different on 5,062 days in 1970–2026.
Juneau: usually 4 hours behind New York; different on 4,881 days in 1970–2026.
Sitka: usually 4 hours behind New York; different on 5,063 days in 1970–2026.
Metlakatla: usually 4 hours behind New York; different on 9,989 days in 1970–2026.
Yakutat: usually 4 hours behind New York; different on 19 days in 1970–2026.
Nome: usually 4 hours behind New York; different on 5,065 days in 1970–2026.
Adak: usually 5 hours behind New York; different on 5,065 days in 1970–2026.
Honolulu: usually 6 hours behind New York; different on 8,613 days in 1970–2026; 5 hours behind today.

Daylight saving periods shared by 5 zones since 1970

Chicago, Denver, Los Angeles, New York and Yakutat have changed their clocks on the same days since 1970. Times are local clock times before each change.

Years	Clocks go forward	Clocks go back	Shift and labels
1974	January 6	October 27	1 hour
1975	February 23	October 26	1 hour
1976–1986	last Sunday in April, 02:00	last Sunday in October, 02:00	1 hour
1987–2006	first Sunday in April, 02:00	last Sunday in October, 02:00	1 hour
2007–2037	second Sunday in March, 02:00	first Sunday in November, 02:00	1 hour

Every change of standard time since 1970

29 changes across the 29 zones, oldest first.

April 29, 1973 Menominee: summer offset kept as standard time
January 6, 1974 Louisville, Kentucky: summer offset kept as standard time
January 6, 1974 Marengo, Indiana: summer offset kept as standard time
October 27, 1974 Louisville, Kentucky: summer offset kept as standard time
October 27, 1974 Marengo, Indiana: summer offset kept as standard time
October 30, 1977 Petersburg, Indiana: summer offset kept as standard time
April 27, 1980 Juneau: summer offset kept as standard time
October 26, 1980 Juneau: summer offset kept as standard time
October 30, 1983 Adak: summer offset kept as standard time
October 30, 1983 Anchorage: summer offset kept as standard time
October 30, 1983 Juneau: UTC−8 to UTC−9
October 30, 1983 Nome: UTC−11 to UTC−9
October 30, 1983 Sitka: UTC−8 to UTC−9
October 27, 1991 Knox, Indiana: summer offset kept as standard time
October 25, 1992 Center, North Dakota: summer offset kept as standard time
October 29, 2000 Monticello, Kentucky: summer offset kept as standard time
October 26, 2003 New Salem, North Dakota: summer offset kept as standard time
April 2, 2006 Knox, Indiana: summer offset kept as standard time
April 2, 2006 Petersburg, Indiana: summer offset kept as standard time
April 2, 2006 Tell City, Indiana: summer offset kept as standard time
April 2, 2006 Vincennes, Indiana: summer offset kept as standard time
April 2, 2006 Winamac, Indiana: summer offset kept as standard time
March 11, 2007 Winamac, Indiana: UTC−6 to UTC−5
November 4, 2007 Petersburg, Indiana: summer offset kept as standard time
November 4, 2007 Vincennes, Indiana: summer offset kept as standard time
November 7, 2010 Beulah, North Dakota: summer offset kept as standard time
November 1, 2015 Metlakatla: UTC−8 to UTC−9
November 4, 2018 Metlakatla: summer offset kept as standard time
January 20, 2019 Metlakatla: UTC−8 to UTC−9

Clock changes in 2026, 2027 and 2028

Adak, Anchorage, Beulah, North Dakota, Boise, Center, North Dakota, Chicago, Denver, Detroit, Indianapolis, Indiana, Juneau, Knox, Indiana, Los Angeles, Louisville, Kentucky, Marengo, Indiana, Menominee, Metlakatla, Monticello, Kentucky, New Salem, North Dakota, New York, Nome, Petersburg, Indiana, Sitka, Tell City, Indiana, Vevay, Indiana, Vincennes, Indiana, Winamac, Indiana, Yakutat
March 8, 2026 (forward 1 hour); November 1, 2026 (back 1 hour); March 14, 2027 (forward 1 hour); November 7, 2027 (back 1 hour); March 12, 2028 (forward 1 hour); November 5, 2028 (back 1 hour)