Daylight Saving Time Explained

Daylight saving time (DST) is the practice of moving clocks forward by one hour in spring and back again in autumn, to shift an hour of daylight from the early morning to the evening. Roughly a third of the world’s countries observe some form of it, mostly at higher latitudes where day length varies a lot through the year.

Spring forward, fall back

In spring, clocks jump forward one hour — so 2:00 a.m. becomes 3:00 a.m., and that day has only 23 hours. In autumn, clocks fall back, repeating an hour and giving a 25-hour day. The common mnemonic is "spring forward, fall back".

The exact dates differ by region. The United States and Canada change on the second Sunday in March and first Sunday in November; the European Union uses the last Sundays of March and October.

Who observes DST

Most of Europe, North America, and parts of the Middle East and Oceania observe DST. Most of Africa and Asia do not, and many equatorial countries never have — near the equator, day length barely changes, so there is little to gain.

Some places have abolished it recently, and the EU has debated ending seasonal clock changes entirely. Because the rules shift over time, always check a current source before scheduling far ahead.

Why it complicates scheduling

DST is the single biggest source of time-zone confusion. When one region has changed its clocks but another has not, the usual difference between them is temporarily off by an hour. A call that is normally at a comfortable time can silently move.

This is why storing times in UTC and converting for display is the safe approach for software, and why a meeting planner that is DST-aware is worth using for recurring international calls.