Uniform Time Act
Great Seal of the United States
Long titleAn Act to promote the observance of a uniform system of time throughout the United States.
NicknamesUniform Time Act of 1966
Enacted bythe 89th United States Congress
EffectiveApril 1, 1967
Public law89-387
Statutes at Large80 Stat. 107
Acts amendedStandard Time Act of 1918
Titles amended15 U.S.C.: Commerce and Trade
U.S.C. sections created15 U.S.C. ch. 6, subch. IX §§ 260–267
Legislative history
  • Introduced in the Senate as S. 1404 by Sens. Gale McGee (DWY) and Norris Cotton (RNH)
  • Passed the House on March 16, 1966 (292–93, in lieu of H.R. 6785)
  • Reported by the joint conference committee on March 30, 1966; agreed to by the House on March 30, 1966 (282–91)  
  • Signed into law by President Lyndon B. Johnson on April 13, 1966

The Uniform Time Act of 1966, Pub. L.Tooltip Public Law (United States) 89–387, 80 Stat. 107, enacted April 13, 1966, was a Law of the United States to "promote the adoption and observance of uniform time within the standard time zones" prescribed by the Standard Time Act of 1918. Its intended effect was to simplify the official pattern of where and when daylight saving time (DST) is applied within the U.S. Prior to this law, each state had its own scheme for when DST would begin and end, and in some cases, which parts of the state should use it.[1]


The law, as originally written, required states that observe DST to begin it at 2 a.m. local time on the last Sunday in April, and to end it at 2 a.m. local time on the last Sunday in October and explicitly preempted all state laws related to daylight saving time per the weights and measures power given to Congress in Article 1, Section 8 of the U.S. Constitution. In 1972, the act was amended to allow states with more than one timezone to exempt only one timezone from DST, in addition to exempting the whole state.[2] The law was later amended again in 1986 to move the uniform start date for DST to the first Sunday in April (effective 1987). The latest amendment, part of the Energy Policy Act of 2005, extends DST by four or five weeks by moving the uniform start date for DST to the second Sunday in March and the end date to the first Sunday in November (effective 2007). The Department of Energy was required to report to Congress the impact of the DST extension by December 1, 2007 (nine months after the statute took effect). The report, released in October 2008, reported a nationwide electricity savings of 0.03% for the year of 2007.[3]


The law does not require that all states observe DST. Individual states may exempt themselves from DST and observe standard time year-round by passing a state law, provided:


observance of daylight saving in Arizona varies

The state of Hawaii has never observed daylight saving, even during World War II when "War Time" was observed by other states as an energy saving measure.

The territories of the Northern Mariana Islands, Puerto Rico, American Samoa, Guam, and U.S. Virgin Islands also do not observe Daylight Saving Time.[4]

Observance of daylight saving varied by county in Indiana, which is divided by the Eastern/Central time zone boundary, until April 2, 2006, when the entire state once again observed DST, a first since Congress repealed the Standard Time Act of 1918.[5]

Arizona has not observed daylight saving since the year following the enactment of the Uniform Time Act of 1966. Native American nations within Arizona may choose. The Navajo Nation has chosen to use daylight saving throughout its territory, which includes parts of New Mexico and Utah where daylight saving is observed. The Hopi Nation, with territory surrounded entirely by the Arizona portion of the Navajo Nation, has chosen not to observe daylight saving.

See also


  1. ^ Jennifer Vernon (March 31, 2006). "The History of Daylight Saving Time". National Geographic. Archived from the original on June 2, 2004. Retrieved June 23, 2012.
  2. ^ An Act to amend the Uniform Time Act to allow an option in the adoption of advanced time in certain cases. Pub. L.Tooltip Public Law (United States) 92–267
  3. ^ Belzer, David B. (October 2008). Impact of Extended Daylight Saving Time on National Energy Consumption. U.S. Department of Energy. "Archived copy" (PDF). Archived from the original (PDF) on May 18, 2013. Retrieved October 21, 2013.((cite web)): CS1 maint: archived copy as title (link)
  4. ^ Jennifer Vernon (March 31, 2006). "The History of Daylight Saving Time". National Geographic. Archived from the original on June 2, 2004. Retrieved June 23, 2012.
  5. ^ Justin L. Mack (March 8, 2019). "Looking back at Indiana's complicated relationship with time: Why Indiana observes daylight saving time". IndyStar. Retrieved November 24, 2020.