Daylight Saving Time (DST) is the practice of setting clocks forward one hour from standard time during the summer months to make better use of natural daylight. The common mnemonic "spring forward, fall back" describes the change.
How DST works
In the spring, clocks "spring forward" by one hour — 2:00 AM becomes 3:00 AM — meaning you lose an hour of sleep but gain an extra hour of evening daylight. In the fall, clocks "fall back" by one hour — 2:00 AM becomes 1:00 AM — meaning you gain an hour of sleep but lose evening daylight. The transition always happens on a weekend (Sunday morning) to minimize disruption to business and transportation schedules.
Which countries observe DST?
About 70 countries observe DST, but most of the world does not. Countries near the equator rarely observe DST because their day length barely changes year-round. In North America, most of the US (except Arizona and Hawaii), Canada (except Saskatchewan), and parts of Mexico observe DST. In Europe, all EU countries observe DST. In the Southern Hemisphere, Australia (most states), New Zealand, Chile, and Paraguay observe DST — but their schedule is reversed (spring forward in October, fall back in March). Asia is almost entirely DST-free — China, India, Japan, South Korea, and most of Southeast Asia do not observe it.
The history of DST
The idea was first proposed by Benjamin Franklin in 1784 (as a joke about saving candles), then seriously by George Hudson in 1895 and William Willett in 1907. Germany was the first country to implement DST on April 30, 1916, during World War I, to conserve coal. The US adopted it in 1918, abolished it in 1919, brought it back during World War II (called "War Time"), and standardized it with the Uniform Time Act of 1966. The US extended DST by 4 weeks in 2007 (starting the second Sunday of March instead of the first Sunday of April).
The debate over DST
DST is increasingly controversial. Proponents argue it provides more evening daylight for outdoor activities, reduces traffic accidents, and benefits retail and tourism. Opponents argue the energy savings are negligible (or even negative in modern buildings with air conditioning), the time changes cause health problems (increased heart attacks, strokes, and workplace injuries in the days following the spring transition), and the disruption to sleep schedules and international business is significant. The US Senate passed the Sunshine Protection Act in 2022 to make DST permanent year-round, but the House has not voted on it. The EU Parliament voted in 2019 to abolish DST, but implementation has been delayed by the COVID-19 pandemic and lack of consensus on whether to keep permanent summer or winter time.
For a complete history and discussion of its effects, read our full article: What is Daylight Saving Time? A Complete Guide.