Direct answer
Daylight saving time shifts the clock forward one hour in spring and back one hour in autumn. The US, Canada, EU, UK, Australia (reversed), and parts of South America observe it; most of Asia, Africa, and equatorial countries do not.
A short history of DST
DST was first proposed by George Hudson in 1895 and first implemented by Germany in 1916 to save coal during WWI. The US adopted it in 1918 and standardized the modern calendar with the Uniform Time Act of 1966.
The original justification — energy savings — is now disputed by modern studies. The political momentum is moving toward permanent standard time in many regions, but the legal calendar has not caught up.
Where DST applies today
About 70 countries observe DST. Adoption clusters in mid-latitudes where summer evenings are noticeably longer than winter ones.
- Observes DST: US (most), Canada (most), EU, UK, Mexico (border zones), Chile, Paraguay, New Zealand, most of Australia.
- Does not observe: Japan, China, India, all of the Middle East, most of Africa, most of South America, Iceland.
- Partially: Arizona (no), Hawaii (no), Saskatchewan (no), Queensland (no).
When the transitions happen
US/Canada: 2nd Sunday in March (forward), 1st Sunday in November (back). EU/UK: last Sunday in March (forward), last Sunday in October (back). Australia: 1st Sunday in October (forward), 1st Sunday in April (back).
Because the US and EU switch on different weekends in spring and autumn, there is a three-week window each transition where the usual offset between New York and London is six hours instead of five. This is the single biggest source of scheduling errors all year.
Business impact
DST disrupts financial market open/close offsets, recurring meeting times, automated alerts, and SLAs. Plan for it.
- Markets: NYSE/Nasdaq always open at 09:30 local — the GMT offset shifts twice a year.
- Recurring calendar events: native invites adjust automatically; hard-coded times do not.
- Cron jobs: schedule in UTC, not local time, to avoid the 02:00 spring-forward gap.
- SLAs: explicitly state the time zone and whether DST applies.
Travel impact
DST affects flight arrival times printed in local time. A red-eye that lands at 06:00 the day after spring-forward effectively lands at 05:00 of yesterday's clock.
- Check whether your destination observes DST before booking ground transport.
- Phones usually update automatically; physical watches and rental-car clocks do not.
- Jet-lag protocols treat the shift as roughly equivalent to a one-hour time-zone change.
Scheduling impact and survival rules
Five rules cover 95% of real-world DST mistakes.
- Always send invites as calendar events, never as plain-text times.
- Re-confirm cross-region recurring meetings during the three-week transition window.
- Audit cron jobs and reports at the start of March and October.
- Use a UTC reference column in dashboards.
- When in doubt, name both zones in the message body.
Frequently asked questions
Why do we still have daylight saving time?
Inertia. The original energy-savings argument is weak in modern grids, and several jurisdictions have passed laws to abolish DST — but coordinated implementation is slow.
Which US states don't observe DST?
Hawaii and most of Arizona (except the Navajo Nation). All US territories — Puerto Rico, US Virgin Islands, Guam, American Samoa, Northern Mariana Islands — also skip it.
When does DST end in 2026?
In the US and Canada, DST ends on 1 November 2026. In the EU and UK, on 25 October 2026. In Australia, DST begins on 4 October 2026.
How does DST affect international meetings?
For a few weeks each spring and autumn, the usual offset between US and European cities is one hour off. Always verify recurring meeting times in March and October.