How time zones work
The world is divided into time zones expressed relative to UTC (Coordinated Universal Time, essentially the successor of Greenwich Mean Time). New York uses Eastern Time: UTC−5 in winter (EST) and UTC−4 in summer (EDT). London uses UTC+0 in winter (GMT) and UTC+1 in summer (BST). The difference between New York and London is therefore usually 5 hours.
Not every country uses daylight saving time, and those that do don't all switch on the same day. That is why the calculator always uses the date you choose. Daylight saving rules come from the time zone database built into your browser; nothing is sent to a server.
Examples
- New York 9:00 → London: on October 6, 2026 it is 14:00 in London, 5 hours later.
- Los Angeles 15:00 → London: 23:00 the same day, 8 hours later.
- London 17:00 → India: 21:30, because India uses UTC+5:30 all year round.
- Amsterdam 20:00 → Tokyo: 03:00 the next day. Japan has no daylight saving time.
- Amsterdam 09:00 → New York on October 28, 2026: 04:00, only 5 hours instead of the usual 6, because Europe switched back on October 25 and the US does so on November 1.
Daylight saving time in the US and Europe
In the United States and Canada, daylight saving time runs from the second Sunday in March to the first Sunday in November, switching at 2:00 local time. In the European Union and the UK, it runs from the last Sunday in March to the last Sunday in October, with all countries switching at the same moment (01:00 UTC). As a result, the gap between North America and Europe is one hour smaller than usual for a few weeks each year: two or three weeks in March and one week around the end of October.
In the southern hemisphere it is the other way around. Sydney observes daylight saving time from October to April, so the gap with London is 11 hours during the northern winter and 9 hours during the northern summer. Most of Arizona and Hawaii do not observe daylight saving time at all.
Times that do not exist
When clocks spring forward, an hour is skipped: in the US, 2:30 on that Sunday does not exist. The calculator then shows a notice and moves the time forward an hour. When clocks fall back, one hour happens twice; the calculator uses the second (standard time) occurrence.
Useful for planning
- Video calls and meetings: always add the time zone to an invitation, or better still, the time in UTC.
- Flights: departure and arrival times on your ticket are local times, so use both time zones to work out the flight duration.
- Family and friends abroad: check that it isn't the middle of the night before you call.
- Shifts and timesheets: total your hours with the hours calculator.
Common US time zones
The contiguous United States has four main time zones: Eastern (New York, Miami), Central (Chicago, Dallas), Mountain (Denver, Phoenix) and Pacific (Los Angeles, Seattle). Alaska and Hawaii each have their own zone.
Frequently asked questions
What is the time difference between New York and London?
Usually 5 hours: when it is noon in New York, it is 17:00 in London. For a few weeks a year, around the daylight saving changes, it is 4 hours.
What is the difference between EST and PST?
Eastern Time is 3 hours ahead of Pacific Time all year, because both switch to daylight saving time on the same day.
What is UTC?
Coordinated Universal Time, the world standard for time. Time zones are written as an offset from UTC, such as UTC+1 or UTC−5.
When does daylight saving time start?
In the US on the second Sunday in March; in Europe on the last Sunday in March.
Does all of China use one time zone?
Yes. All of China officially uses UTC+8 without daylight saving time, even in the far west of the country.
Is the converter correct for future dates?
Yes, as long as the daylight saving rules do not change. Countries occasionally change their rules; your browser's time zone database is updated with browser and system updates.
Last reviewed: 2026-10-06. Results are estimates for information only.