What Is Daylight Saving Time (DST)?
One-line definition: DST is the practice of moving clocks forward by one hour in spring (“spring forward”) and back by one hour in autumn (“fall back”) to shift usable daylight to evening hours during summer.
How Daylight Saving Time Works
In spring, clocks move forward one hour — 2:00 AM becomes 3:00 AM. That hour “disappears.” Sunset is now an hour later in the evening, extending usable daylight for outdoor activities and reducing energy consumption (the original justification).
In autumn, clocks move back one hour — 2:00 AM becomes 1:00 AM. That hour repeats. Sunrise and sunset return to earlier times, aligning with the shorter days of winter.
How DST Affects UTC Offsets
UTC itself never changes. What changes is the offset that a local timezone applies to UTC.
| Zone | Winter (Standard) | Summer (Daylight) |
|---|---|---|
| New York (EST/EDT) | UTC-5 | UTC-4 |
| Chicago (CST/CDT) | UTC-6 | UTC-5 |
| London (GMT/BST) | UTC+0 | UTC+1 |
| Paris (CET/CEST) | UTC+1 | UTC+2 |
| Sydney (AEST/AEDT) | UTC+10 | UTC+11 |
| India (IST) — no DST | UTC+5:30 | UTC+5:30 |
| Japan (JST) — no DST | UTC+9 | UTC+9 |
Which Countries Don't Use DST?
The majority of the world does not observe DST. Countries on fixed UTC offsets year-round include: India, China, Japan, South Korea, Singapore, UAE, most of Africa, the Philippines, Indonesia, Thailand, Vietnam, and more.
In the US, Arizona (except the Navajo Nation) and Hawaii opt out. In the EU, there have been ongoing discussions about abolishing DST — but as of 2026, EU member states still observe it. See the DST 2026 dates page for this year's exact switch dates across all major regions.
Frequently Asked Questions
What is the difference between DST and standard time?
Standard time is the timezone's default UTC offset — EST (UTC-5), for example. DST is the shifted version — EDT (UTC-4). DST is active in summer; standard time is active in winter. The abbreviation changes from S (Standard) to D (Daylight) when DST is in effect.
Does DST affect UTC?
No. UTC never changes for DST. The offset that local timezones apply to UTC is what shifts. UTC stays fixed at UTC+0 year-round.
When does DST start and end?
In the US: second Sunday in March (start) and first Sunday in November (end). In the UK/EU: last Sunday in March and last Sunday in October. Australia's DST runs October to April — the opposite season, because Australia is in the Southern Hemisphere.
Why is it called "Daylight Saving Time" (not "savings")?
The official name is "Daylight Saving Time" — singular, not savings. Both forms are used colloquially, but the federal US statute and most style guides use "Saving" without the S.