Daylight Saving Time is observed in the U.S. beginning at 2 a.m. on the second Sunday in March, and ends at 2 a.m. on the first Sunday in November.

Barring any further modifications to DST, the following are the dates Daylight Saving Time will be in effect in the United States:

Setting your clock ahead one hour of standard time provides more daylight at the end of the day during late spring, summer, and early fall. Daylight Saving Time provides more accessible daylight hours for those working outdoors, such as farmers, as well as a safer commute home for most workers.

Until recently, Daylight Saving Time in the United States had been observed from the first Sunday in April to the last Sunday in October. In 2007, a new U.S. Federal law went into effect and it was henceforth observed from the second Sunday in March to the first Sunday in November, adding about a month to Daylight Saving Time.

Most areas in Arizona, Hawaii and the U.S. territories of Puerto Rico, Virgin Islands, Guam, and American Samoa, do not observe DST, but instead stay on "standard time" all year long. Indiana was another state that was only partially on DST until 2006.

The rule to remember when setting your clocks is, spring forward one hour in the spring, and fall back one hour in autumn.


NOTE: A number of sources incorrectly refer to it as "Daylight Savings Time." It is properly referred to as Daylight Saving (singular) Time, not Daylight Savings (plural) Time.

Energy savings was one of the most prominent advantages the experts used to argue in favor for implementing, and later, expanding the use of Daylight Saving Time in the United States. The contention was that moving our clocks ahead one hour, would cut the amount of electricity we consume each day by reducing the need for electrical lighting by one hour each evening. Studies conducted in the 1970s by the U.S. Department of Transportation concluded that we reduce the entire country's electrical usage by about one percent each day during Daylight Saving Time. California Energy Commission studies later confirmed a savings of about one percent per day.

Experts also argued that Daylight Saving Time saves lives and prevents traffic injuries by allowing more people to travel home from work and school in daylight, which is much safer than darkness. The U.S. Department of Transportation estimated that 50 lives were saved and about 2,000 injuries were prevented in March and April of the study years. The department also estimated that $28 million was saved in traffic accident costs. Another contention was that Daylight Saving Time prevents crime. Because people get home from work and school and complete more errands and chores in daylight, Daylight Saving Time would seem to reduce people's exposure to various crimes, which are more common in darkness than in light.

A more recent in-depth University of California study contradicted the earlier findings and showed that Daylight Saving Time actually raises utility bills. The USC study concluded that Americans were each spending $3.19 more per year as a result of Daylight Saving Time. This seemingly minuscule increase adds up to hundreds of millions of dollars in additional energy usage in America each year. Likewise, earlier claims of safety and crime prevention under DST have now been challenged.

The USC study revealed that the amount of electricity used to power light bulbs did indeed drop when DST was observed. But it also established that overall electrical usage increased as a result of additional use of air-conditioning because more people were home on hot afternoons when they would have otherwise still been at work. The additional hour of darkness on cool mornings also caused an increase in the use of heaters.

The USC study was not the first to question the claim of energy savings under Daylight Saving Time. Back in the 1970s, the National Bureau of Standards concluded that there was no significant energy savings when DST was observed.

Additional study of the issue is obviously warranted.

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