US vs EU daylight saving dates

Two different Sundays

Under current US federal rules, daylight saving starts on the second Sunday in March and ends on the first Sunday in November. The EU still uses the last Sunday in March and the last Sunday in October. The United Kingdom follows the EU calendar even after Brexit, via UK statute aligned to those Sundays.

That produces two mismatch windows: late March, when America has already sprung forward and Europe has not, and late October, when Europe has fallen back and America has not. In those weeks the usual six-hour Paris–New York gap becomes five or seven hours depending on the direction of the lag.

Australia and New Zealand run daylight saving in the opposite season. Their mismatch with both the US and Europe is measured in months, not a week.

What to do with a standing invite

Anchor the event in one named IANA zone, not in “15:00 CET / 09:00 EST.” Calendar software that stores a zone id will move the wall time correctly on each side; a pair of frozen offsets will not.

The week after each mismatch, open the two city pages — for example Paris and New York — and read the live gap and the next transition date. Recurring series that were created years ago with a Windows “Eastern Time (US & Canada)” plus a floating CET are the ones that surprise people.

If the EU ever stops changing clocks, as it has discussed, the March and October traps disappear on the European side only. The US rule would still move. Do not bake “always six hours” into a runbook.

How NowZones shows the lag

Difference pages for transatlantic curated pairs render the DST story in prose, not only as two ticking clocks. When both cities change, the copy names both dates. When only one side moves, it says so.

City pages list the next transition when the zone observes DST. Use that, then convert a sample 09:00 through the converter on a date inside the mismatch week if you need a one-off check.