Daylight saving time: US states and territories where the clocks do not change

Most Americans have to change their clocks twice a year: on the second Sunday in March, when they switch to daylight saving time and then move forward an hour, and again on the first Sunday in November, when they move back an hour again.

There are notable exceptions to this rule, however, with two U.S. states and five territories setting their clocks to the same time for all or most of the year.

Hawaii and Arizona do not observe daylight saving time, with the exception of the Navajo Nation, which includes parts of New Mexico and Utah.

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Likewise, the U.S. territories of Puerto Rico, Guam, American Samoa, the Northern Mariana Islands and the U.S. Virgin Islands observe the same time all year round.

In states and territories near the equator, such as Hawaii and Puerto Rico, the change in solar radiation between seasons is far less intense than further north, largely defeating the purpose of switching between standard time and daylight saving time.

Tododisca, a health website, said most of Arizona has opted not to adopt daylight saving time because of its “extremely hot climate.” The website added: “By neither moving the clocks forward nor back, the state minimizes heat stress during the hottest times of the day, resulting in less energy used for cooling.”

According to the Department of Defense, Congress passed the Standard Time Act in 1918, which was designed to “provide additional daylight hours per day to save on energy costs during World War I.” The act was later repealed, although another Daylight Saving Time Act was passed in 1942 “to save fuel” and “promote national security and defense” during World War II.

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In 1966, Congress passed the Uniform Time Act, which implemented daylight saving time across the country from the last Sunday in April through the end of October. However, Hawaii and most of Arizona opted not to use it.

The U.S. Department of Defense website stated: “Parts of the law have been changed several times since then, including the dates for the spring and fall time changes.”

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“The current arrangement was introduced in 2005 by President George W. Bush and extended daylight saving time by several weeks. It now begins on the second Sunday in March and ends on the first Sunday in November.”

However, daylight saving time remains controversial. In 2020, the American Academy of Sleep Medicine published a statement in Journal of Clinical Sleep Medicine and calls for its abolition.

“The United States should abolish seasonal time changes in favor of a nationwide, fixed, year-round time,” the organization demanded.

“Current evidence strongly supports the adoption of a year-round standard time that is most consistent with human circadian biology and provides clear public health and safety benefits,” it said.

In May PLOS Computational Biology A scientific journal published a study entitled “Measurable health effects associated with daylight saving time,” which states: “Daylight saving time is beneficial for energy conservation, but at the same time it has been reported to increase the risk of cerebrovascular and cardiovascular problems.”

Nevertheless, nearly 20 states have passed laws or resolutions calling for permanent adoption of daylight saving time, starting with Florida in 2018. These proposed changes cannot be implemented without the approval of Congress.