Daylight saving time: why your meeting moved
A London–New York call is usually five hours apart. For a few weeks, it isn’t. Here is how to stop a calendar surprise.
Two clocks, two changeover dates
Imagine a team that meets every Tuesday at 15:00 in London. On 3 March 2026, that is 10:00 in New York. On 10 March, the same London appointment is 11:00 in New York. Neither organizer edited the invitation. New York moved to daylight saving on 8 March; London does not move until 29 March. Between those dates, the gap is four hours instead of five. The mismatch is a calendar effect, not a broken clock.
A time zone is a set of rules
“UTC−5” describes an offset. “America/New_York” describes a named time zone whose offset depends on the date. They are not interchangeable. Store a recurring 09:00 New York stand-up with the named zone if it should follow the local working day. Store an instant when you mean one particular moment worldwide. A fixed UTC recurrence and a fixed local-time recurrence can produce different schedules after the clocks change.
The invitation needs an anchor
Choose which location owns the meeting time. Then preview a date before and after each participant’s next clock change. A one-off calendar event can safely identify its start in UTC: each calendar converts that instant locally. A recurring invitation needs its recurrence rules and zone preserved too. Our converter downloads a single one-hour event, not a recurring series. For a weekly series, set the recurrence and home time zone in your calendar application.
Try the awkward week
Compare 15:00 Europe/London with America/New_York on 3 March, 10 March, and 31 March 2026. The New York results are 10:00, 11:00, and 10:00 under the applicable rules. Then try a colleague in Tokyo, where the clocks do not make those seasonal changes. This is why “same time next week” needs a home time zone. Rules can change, so use an updated browser and check the actual meeting date before sending the invitation.
Test your intuition
Sources & further reading
Original explanations with worked examples. Reference links point to the underlying standards and documentation.