Daylight Saving Time 101 | National Geographic

In spring, we move our clocks forward an hour, and in fall, we move them back an hour. That section in between, we call that daylight savings time. And oh, it's singular; sorry, I mean daylight saving time. It may seem pretty straightforward, but daylight saving time has both serious repercussions and major benefits.

In the United States of America, 48 states observe daylight saving time, with Hawaii, most of Arizona, and the U.S. territories of Guam, American Samoa, Puerto Rico, and the U.S. Virgin Islands choosing to ignore it. In spring, the 48 states all jump ahead an hour, and the immediate effects can be disastrous. One study found that the average American worker loses 40 minutes of sleep when the clock springs forward. That means lots of people could be losing an hour of sleep or more on the same night, essentially giving us all jet lag.

Sleep deprivation can lead to serious health issues. According to studies, the first Monday of daylight saving time has 25% more heart attacks than a typical Monday. Car accidents go up 17% in the days after the time shift, and workplace accidents go up about six percent. Workers are 67% more likely to miss work due to these accidents, and productivity goes way down the first Monday after daylight saving time.

Daylight saving time isn't even universal. Fewer than half of the countries in the world actually use it, and few agree on when it starts or ends. The switch to daylight saving time has a lot of negatives, so why do we do it at all? The real reason we kept daylight saving time and extended it? Economics. Some studies suggest we spend money when it's sunny outside. If it's light out after work or school, people spend more at the shops.

From 1968 to 1971, the UK kept their version of daylight saving time for the whole year, and traffic deaths declined by 11% because it was light after work during the winter. Another recent study found that kids are more likely to exercise outside during the winter daylight saving time rather than huddling inside after school.

With benefits and negative effects, it's no wonder daylight saving time has opponents and supporters. But on what side of the clock do you stand?