Daylight Saving Time
When does DST start and end? Which countries observe it? Why do some countries not? Everything you need to know about Daylight Saving Time worldwide.
Daylight Saving Time (DST) — called Summer Time in British English — is the practice of advancing clocks by one hour during the warmer months of the year. The goal is to shift an hour of daylight from the early morning, when most people are asleep, to the evening, when they are awake and active. In spring, clocks move forward one hour ("spring forward"), and in autumn they move back one hour ("fall back").
The idea was first seriously proposed by New Zealand entomologist George Hudson in 1895 and independently by British builder William Willett in 1907. Germany became the first country to implement DST nationally in 1916, as a wartime energy-saving measure. Most of Europe and North America followed. Today, approximately 70 countries observe DST, while the majority of the world does not.
The majority of the world's countries do not observe Daylight Saving Time. Most of Asia, Africa, and the equatorial regions of South America have never adopted it or have abandoned it. Countries close to the equator experience relatively consistent sunrise and sunset times year-round, making the adjustment less meaningful. Several major countries abolished DST in the past decade, citing minimal energy savings and documented health impacts from the biannual clock change.
The original energy-saving rationale for DST has been largely undermined by modern research. Multiple studies have found that the energy savings from DST are minimal or nonexistent, because the electricity saved on lighting is offset by increased use of air conditioning in the warmer evenings. A 2008 study of Indiana — which only adopted DST statewide in 2006 — found that DST actually increased residential electricity consumption by 1 to 4 percent.
Beyond energy, research has documented a range of health effects associated with the biannual clock change. The spring transition, which causes people to lose one hour of sleep, is associated with a measurable increase in heart attacks, traffic accidents, and workplace injuries in the days immediately following the change. The disruption to circadian rhythms — the body's internal clock — can take several weeks to fully resolve.
The European Parliament voted in 2019 to end mandatory DST across the EU, but the change has not been implemented as of 2026 due to disagreements between member states about which permanent time to adopt. In the United States, the Sunshine Protection Act — which would make DST permanent — has been introduced in Congress multiple times but has not passed. Russia abolished DST in 2014 and moved to permanent standard time. Brazil abolished DST in 2019. Turkey moved to permanent summer time in 2016.
The core challenge in abolishing DST is the choice of which permanent time to adopt. Permanent summer time gives more light in the evenings but darker mornings in winter. Permanent winter time gives lighter mornings but darker evenings. Neither option is universally preferred, and the debate about which to choose is often as contentious as the debate about whether to abolish DST at all.
When a country observes DST, its UTC offset changes by one hour for the duration of the summer period. New York is UTC-5 (Eastern Standard Time) in winter and UTC-4 (Eastern Daylight Time) in summer. This means the time difference between New York and Tokyo changes from 14 hours in winter to 13 hours in summer. For anyone scheduling international meetings or calls, it is essential to check whether both locations are currently observing DST, as the offset between them can change by one or even two hours depending on the timing of each country's transition.