Why meeting times shift twice a year, and how to find overlap
A meeting time shifts for a few weeks each spring and autumn because countries change their clocks on different dates. A time that worked last month can be an hour out, or leave a gap of four hours instead of five, for part of the year. Use named time zones rather than fixed offsets, so the tool applies the right rule for each date.
Time zone converterWhat time is it there?OpenWhy the dates do not match
Daylight saving time (DST) moves the clock forward in spring and back in autumn. Each country sets its own rule. In 2026:
- United States. Clocks go forward on the second Sunday in March, which was 8 March 2026, and back on the first Sunday in November, which was 1 November 2026.
- European Union and United Kingdom. Clocks go forward on the last Sunday in March, which was 29 March 2026, and back on the last Sunday in October, which was 25 October 2026.
Because the US and Europe change on different dates, the gap between New York and London changes for a few weeks in March and again for about a week in autumn. Other countries follow other rules, and many do not use DST at all, including Japan, China and India.
Time zones and UTC offsets
A UTC offset is the number of hours a time is ahead of or behind Coordinated Universal Time (UTC). The offset is a fixed number for a given zone at a given moment, but it changes when DST starts and stops. New York is UTC−5 in winter and UTC−4 in summer. London is UTC+0 in winter and UTC+1 in summer.
Named zones such as America/New_York or Europe/London carry the whole history of the rule, so a converter using them gets the date right automatically. A fixed offset such as UTC−5 is correct for part of the year only. Use a fixed offset only when you know the rule will not change for the period you are scheduling.
A worked example of the gap
Take 12:00 in New York and 12:00 in London, on a few dates in 2026:
| Date | New York | London | Gap |
|---|---|---|---|
| 5 March | 12:00 EST (UTC−5) | 12:00 GMT (UTC+0) | London is 5 hours ahead |
| 15 March | 12:00 EDT (UTC−4) | 12:00 GMT (UTC+0) | London is 4 hours ahead |
| 28 October | 12:00 EDT (UTC−4) | 12:00 GMT (UTC+0) | London is 4 hours ahead |
| 5 November | 12:00 EST (UTC−5) | 12:00 GMT (UTC+0) | London is 5 hours ahead |
Between 8 and 28 March, the gap is four hours rather than five, because the US has started DST and Europe has not. In autumn the pattern reverses. From 25 October to 1 November, Europe is back on standard time while the US is still on daylight time, so the gap is four hours again.
Finding working-hour overlap
A meeting works when both people are in working hours. Suppose you work 09:00 to 17:00 in New York, and a colleague works 09:00 to 17:00 in London.
- In mid-January, when both are on winter time, London 09:00 is New York 04:00. The London working day runs from 04:00 to 12:00 in New York, so the overlap with New York's 09:00 to 17:00 is 09:00 to 12:00, which is three hours.
- In mid-March, between the US and European changes, London 09:00 is New York 05:00. The London day runs from 05:00 to 13:00 New York time, so the overlap is 09:00 to 13:00, which is four hours.
The overlap changes by an hour for a few weeks, so a meeting time that was comfortable in February may be early for one person in March. Check the overlap on the actual dates of the meeting, not the usual ones.
Steps for scheduling across zones
- Name both zones, such as America/New_York and Europe/London, rather than writing UTC−5.
- Pick the date of the meeting, not today's date, and let the converter apply the correct offset.
- Find the overlap in both zones, and write the time in each.
- Send the meeting invitation with the zone named, so the calendar converts it correctly for each person.
- If the meeting repeats, check it again after each clock change.
The time zone converter does steps 1 to 3 for any pair of places.
Edge cases
- Calendars that were created before a rule changed. A recurring event set years ago can move when a country changes its DST rule. Check that the calendar is storing the zone, not a fixed offset.
- The night of the change. Some local times do not exist on the spring change, and some occur twice on the autumn change. Avoid scheduling in the hour that does not exist, or the hour that repeats.
- Places without DST. A place such as Arizona, which mostly does not use DST, stays on the same offset all year, so the gap with a DST place changes twice a year.
- Shared dates near midnight. A meeting at 23:30 in one zone is already the next day in another, so check the date as well as the time.
Quick answers
Why does the time difference between New York and London change?
Because the United States and Europe change their clocks on different dates. For a few weeks each spring and autumn, the gap is an hour smaller or larger.
Should I write UTC−5 or America/New_York in an invitation?
Use the named zone, since it follows the DST rule for the date of the meeting. A fixed offset is correct only for the part of the year you are working in.
Which countries do not use daylight saving time?
Many do, including Japan, China and India, which keep the same offset all year. Check a current source for a specific place, since rules change.
