Standards: Daylight Saving Time (DST)

Most people in the U.S. will turn their clocks back one hour at 2 AM local time on Sunday, Nov. 6. But Hawaii, most of Arizona, and some U.S. territories do not observe Daylight Saving Time

Daylight Saving Time (DST) is a widely used system that adjusts the official local time forward from theofficial standard time during summer months, usually by one hour.

The Energy Policy Act of 2005 changed the start and end dates of Daylight Saving Time in the United States. As of 2007, DST begins on the second Sunday in March and ends on the first Sunday in November. The U.S. Department of Energy (DOE) is studying the impact of this DST extension, and theU.S. Congress retains the right to revert to the previous DST schedule if the study shows it does not produce a significant savings of energy.

Use of Daylight Saving Time in the United States, is governed by the Uniform Time Act of 1966. This Act provides a standard for establishing the dates when DST begins and ends in the U.S., while allowing local exemptions from its observance. States wishing to be exempt from DST may pass a law exempting the entire state. The states of Arizona and Hawaii do not observe DST. However, the Navajo Indian Reservation in Arizona does. In addition, American Samoa, Guam, the Northern Mariana Islands, Puerto Rico, and the U.S. Virgin Islands do not observe DST.

Approximately 70 countries observe DST.

Additional Resources:

• Daylight Saving Time Rules
• Time Exhibits
• The Seasons: Spring, Summer, Fall and Winter
• Standards: Leap Year