Daylight Saving Time (DST), Fully Explained
How the practice of setting clocks forward an hour in summer works, and why different countries apply it differently.
What is daylight saving time?
Daylight saving time (DST) is the practice of setting clocks forward one hour in summer to make better use of daylight. It starts in spring and ends in autumn.
Why time-difference calculations get confusing
Countries that observe DST change their UTC offset twice a year. New York, for example, is UTC−5 in winter and UTC−4 in summer. Seoul and Tokyo, on the other hand, have no DST and always keep a fixed offset.
- Observe DST: the United States, most of Europe, parts of Australia
- No DST: South Korea, Japan, China, India, and most equatorial regions
A world clock that handles it automatically
World Clock uses your browser's IANA time-zone data, so each city's DST status and transition dates are applied automatically. There's no need to calculate anything yourself.
When scheduling international meetings, pay special attention to the DST transition weeks (in March, November, and so on).