DST Calculator

What Is Daylight Saving Time?

Daylight Saving Time (DST) is the practice of advancing clocks by one hour during the warmer months of the year so that evening daylight lasts one hour longer while sacrificing an hour of morning daylight. People often use the phrases "spring forward" (when clocks gain one hour) and "fall back" (when clocks revert to standard time) to remember which direction the clocks move.

The origins of DST trace back to an 1895 proposal by New Zealand entomologist George Vernon Hudson, who wanted more daylight after work hours to pursue his hobby of insect collecting. Germany became the first country to officially adopt it in 1916 during World War I, primarily to conserve coal used for lighting. Britain, France, and many other nations quickly followed. Today, approximately 70 countries observe DST, though the specific dates, rules, and even the question of whether to keep it remain politically contentious worldwide.

How DST Works

In countries that observe DST, clocks are typically moved forward by one hour in spring, meaning there is one less hour of darkness in the evening. In autumn, the clocks revert, giving back that hour. The net result is that sunrise and sunset both occur approximately one hour later in the clock-based sense during DST, but the total length of daylight does not change — only the labelling of when it occurs shifts.

The transition does not happen simultaneously worldwide. The United States springs forward on the 2nd Sunday of March and falls back on the 1st Sunday of November. The European Union uses the last Sunday of March and last Sunday of October. Australia (where DST is a summer phenomenon in the southern hemisphere) moves clocks forward in October and back in April.

Which Countries Observe DST in 2025?

Approximately 70 countries observe DST in 2025, including all of the continental United States and Canada (with some provincial and state exceptions), virtually all of the European Union, much of South America's temperate zones, Australia's eastern and southern states, New Zealand, and Israel. Countries that do not observe DST include all of Asia's most populous nations (China, India, Japan, South Korea, Indonesia), Russia, most of Africa, and the equatorial regions where day length varies little throughout the year.

Notable DST Facts

• India has never observed DST in its history. IST (UTC+5:30) is fixed year-round.
• China observed DST from 1986 to 1991, then abolished it permanently.
• Russia permanently abolished seasonal clock changes in 2014, adopting year-round "winter time."
• Arizona (USA) does not observe DST, except for the Navajo Nation within its borders.
• Brazil abolished DST in 2019 after decades of observance in its southern states.
• The EU voted in 2019 to end mandatory DST but has not yet passed a directive enforcing the change.
• Queensland, Western Australia, and the Northern Territory do not observe DST within Australia.

Why UTC Offsets Change During DST

Standard time (winter time) is a timezone's base UTC offset. For example, New York on standard time is UTC-5 (Eastern Standard Time, EST). When DST is active, New York advances to UTC-4 (Eastern Daylight Time, EDT). The timezone name changes, but the geographic location of course does not. This is why applications, databases, and APIs that handle international scheduling must use IANA timezone identifiers (like "America/New_York") rather than fixed UTC offsets — the offset changes twice a year.

Practical Impact of DST

For travelers, remote workers, and anyone scheduling international meetings, DST creates real complexity. A regular 9 AM New York call with a London colleague may shift by an hour relative to London time for several weeks each year, because the US and EU don't change their clocks on the same dates. The gap between New York and London is normally 5 hours, but briefly becomes 4 or 6 hours during the transition weeks in March and October when one jurisdiction has changed and the other has not yet done so. Our multi-city comparison tool helps you visualise exactly this scenario.

DST Transition Dates for 2025 and 2026

Frequently Asked Questions