Daylight saving time (abbreviated DST), commonly referred to as daylight savings time in speech,[1] and known as summer time in some countries, is the practice of advancing clocks during summer months so that evening daylight lasts longer, while sacrificing normal sunrise times. Typically, regions that use daylight saving time adjust clocks forward one hour close to the start of spring and adjust them backward in the autumn to standard time.[2]

George Hudson proposed the idea of daylight saving in 1895.[3] The German Empire and Austria-Hungary organized the first nationwide implementation, starting on April 30, 1916. Many countries have used it at various times since then, particularly since the energy crisis of the 1970s.

DST is generally not observed near the equator, where sunrise times do not vary enough to justify it. Some countries observe it only in some regions; for example, southern Brazil observes it while equatorial Brazil does not.[4] Only a minority of the world’s population uses DST, because Asia and Africa generally do not observe it.

DST clock shifts sometimes complicate timekeeping and can disrupt travel, billing, record keeping, medical devices, heavy equipment,[5] and sleep patterns.[6] Computer software often adjusts clocks automatically, but policy changes by various jurisdictions of DST dates and timings may be confusing.[7]