This Sunday, people across the country will set their clocks forward an hour, marking the start to Daylight Saving Time. But it hasn’t always happened on the second Sunday in March. The Energy Policy Act of 2005, which was implemented in 2007, added four weeks to Daylight Saving Time by changing it to start on the second Sunday in March and end on the first Sunday in November.

How much energy does Daylight Saving Time save? In 2008, Energy Department experts studied the impact of the extended Daylight Saving Time on energy consumption in the U.S. and found that the extra four weeks of Daylight Saving Time saved about 0.5 percent in total electricity per day. While this might not sound like a lot, it adds up to electricity savings of 1.3 billion kilowatt-hours -- or the amount of electricity used by more than 100,000 households for an entire year.