When does Daylight Saving Time start?

A short history of DST start dates

In May 2026, a Chicago schoolteacher walks into homeroom on a Monday after spring-forward weekend and watches half the class arrive late because parents forgot to advance the clocks. The rule she should have circulated: in the United States, DST begins on the second Sunday of March at 2:00 AM local time. That sentence is the answer this tool produces in one click, but the rule behind it has a 120-year history.

Benjamin Franklin's 1784 satirical letter to the Journal of Paris is the popular origin myth, but the practice did not exist as policy until German engineer Willett and New Zealand entomologist George Hudson independently proposed it around 1907. The first national adoption came on April 30, 1916, when Imperial Germany advanced clocks to save coal during the First World War. The United States followed with the Standard Time Act of March 19, 1918, abolished the policy a year later under farmer pressure, and re-imposed it during World War II as "War Time".

The modern US framework comes from the Uniform Time Act of 1966, which standardised the start (last Sunday of April) and end (last Sunday of October) but allowed states to opt out. Arizona and Hawaii opted out. Indiana, until 2006, was a famous mosaic where some counties observed and others did not. The 1986 amendment moved the start to the first Sunday of April. The current rule — 2nd Sunday March → 1st Sunday November — is the Energy Policy Act of 2005, in force from 2007. That extension added four weeks of evening daylight in spring and one week in fall, on the theory that 0.5% of US electricity demand could be shifted from peak evening hours.

Europe arrived at its harmonised rule later. After patchwork national policies through the 1970s, EU Directive 2000/84/EC codified the all-Union rule: start on the last Sunday of March at 01:00 UTC, end on the last Sunday of October at 01:00 UTC. The UTC anchor is the elegant part — it means every member state jumps simultaneously rather than over a four-hour cascade. The European Parliament voted in March 2019 to abolish seasonal time changes, but the implementing legislation has been stuck since on whether the bloc settles on permanent summer or winter time.

Southern-hemisphere DST runs opposite. Australia begins on the first Sunday of October in NSW/VIC/TAS/ACT/SA and ends on the first Sunday of April. New Zealand starts on the last Sunday of September. Chile and Paraguay observe in September-October. Brazil, after operating DST for nearly a century, suspended it in 2019 because the country's air-conditioning load no longer aligns with the clock. Mexico abolished DST in 2022, with only border municipalities retaining it for US-alignment.

All of this is encoded in the IANA Time Zone Database, originally written by Arthur David Olson in 1986 on a Bell Labs minicomputer. The TZDB lives at data.iana.org/time-zones; every Linux distribution, every JVM, every Postgres install, and every Google data center compiles its zic output. When a country changes DST mid-year (Egypt did in 2014; Russia in 2014; Iran in 2022), the TZDB ships a patch the next day and the world updates. This tool consults the same standing rules — second Sunday, last Sunday, first Sunday — that the TZDB itself encodes in its Rule records.

See also DST end date, timezone map and leap year checker.