When Do Clocks Change and Move Forward? Daylight Saving Time 2021 Details

In 2021, daylight saving time (DST) begins on March 14 at 2 a.m. local time. This means clocks will move forward by one hour on this day, so at 2 a.m., the time shifts to 3 a.m. DST happens on the second Sunday of March every year at the same time.

The switch back to standard time takes place on the first Sunday of every November at 2 a.m. local time. Clocks move back by an hour, so at 2 a.m., the time becomes 1 a.m.

For most electronic devices, such as computers and mobile phones, the DST update takes place automatically.

The National Institute of Standards and Technology (NIST) says: "There shouldn't be any problems if your operating system has the latest updates. All NIST time services broadcast Coordinated Universal Time (UTC).

"Corrections for your local time zone and for daylight saving time are provided by your computer's operating system. Therefore, it is important that you have the latest software updates for your operating system," it adds.

Why is daylight saving time observed?

Since the daylight period begins an hour later in the morning and lasts an hour longer in the evening, "this change helps keep the hours of daylight coordinated with the time that most people are active," NIST explains.

"Proponents feel that this saves energy because in the spring and summer months more people may be outside in the evening and not using energy at home," according to NIST.

Where is daylight saving time observed?

DST was introduced in the U.S. in 1918 and it is observed in most of the country except in Hawaii, American Samoa, Guam, Puerto Rico, the Virgin Islands and most of Arizona. The Navajo Indian Reservation in Arizona does observe DST.

The rules for the dates of DST were defined by The Uniform Time Act of 1966 and all regions that observe DST use the same transition days. However, the act also allows states to legislatively decide whether to practice it or not.

"The date rules sometimes change, most recently in 1986 and 2007, extending the length of DST. The Department of Transportation (and not NIST) oversees and regulates DST," NIST states.

Many countries around the world also practice a version of DST and the dates for the time changes may vary from the dates observed in the U.S.

"There is no single body that regulates time zones or daylight saving time around the world. Some countries provide little or no notice when they change their DST status and/or date rules," NIST says.

Clock Florida daylight saving time 2007
A person adjusting the time on a clock at the end of the day light saving time period on November 2, 2007 in Plantation, Florida. Joe Raedle/Getty Images