Twice a year, many countries move their clocks by one hour. It sounds simple, but it confuses a lot of people - Especially when you're trying to call someone in another country. Here's the plain-English version.
Key points
- Daylight saving time (DST) moves the clock forward one hour in spring and back one hour in autumn.
- The goal is to shift daylight into the evening, when more people are awake.
- DST changes a place's UTC offset, so time differences between countries shift by an hour for part of the year.
- Not everyone uses it - Many countries near the equator don't.
What daylight saving time actually does
Daylight saving time moves the clock so there's more daylight in the evening and less in the early morning. Twice a year, the clocks jump by one hour:
| Season | What happens | Memory trick | Effect on you |
|---|---|---|---|
| Spring | Clocks go forward 1 hour | "Spring forward" | You lose an hour of sleep |
| Autumn | Clocks go back 1 hour | "Fall back" | You gain an hour of sleep |
The exact dates change from year to year and from country to country, which is part of why DST trips people up.
Why it matters for time zones
When a place is on DST, its UTC offset changes. UTC is the world's base time, and an offset is how many hours a place is ahead of or behind it.
For example, New York is UTC−5 in winter and UTC−4 in summer. So the time difference between New York and a place that doesn't use DST will shift by an hour, depending on the season. That's why a call that's "5 hours apart" in January might be "4 hours apart" in July.
You can always check the live difference on any city page or use our time zone converter to do the math for you.
Who uses daylight saving time?
- Most of the United States, Canada, Europe and parts of Australia use it.
- Many countries near the equator don't - Their daylight barely changes through the year, so there's little to gain.
- Some places have stopped using it entirely.
Every time zone page on Alarm.now tells you whether that zone changes its clocks, so you never have to guess. Browsing a specific country? Open its country page to see its daylight saving status at a glance.
How to never get caught out
- Check the current time in the other place right before you schedule a call - Don't rely on memory.
- Remember that two places can change clocks on different dates, so the gap between them can be "off" for a week or two each year.
- Once you know the right time, set an alarm so you don't miss it.
A quick example
Say you're in London and want to call a friend in New York at their 9:00 AM.
- In winter, London is 5 hours ahead, so you'd call at 2:00 PM your time.
- In summer, the gap is the same 5 hours for a few weeks - But because the two regions switch on different dates, there are short windows where it's only 4 hours. When in doubt, convert it.
TL;DR
Daylight saving time moves the clock one hour forward in spring and back in autumn to make better use of evening daylight. It changes a region's UTC offset, which is why time differences between countries shift by an hour during part of the year. Not sure of the current gap? Use the time zone converter or check any world city.
Frequently asked questions
When do the clocks change for daylight saving time?
The clocks go forward one hour in spring and back one hour in autumn. The exact dates vary by country and year, so check a calendar close to the date.
Which countries use daylight saving time?
Most of the United States, Canada, Europe and parts of Australia use it. Many countries near the equator do not, because their daylight barely changes through the year.
Why does the time difference between two countries change?
Because daylight saving shifts a country's UTC offset for part of the year. If one country changes its clocks and the other does not, the gap between them moves by an hour.