Daylight saving time, explained without the headache

Twice a year, half the world moves its clock by an hour and the other half watches in mild bafflement. If you schedule meetings across regions, DST is the single most common reason a recurring event silently moves on someone's calendar.

What DST actually is

Daylight saving time shifts local clocks forward by one hour in the spring and back by one hour in the autumn. The original idea — popularized in the early 20th century — was to make better use of evening daylight. Whether it still does that is a debate every parliament seems to have every five years.

Who still does it?

Roughly speaking: most of Europe, the United States, Canada, Mexico (partially), parts of South America, and a handful of others. Most of Asia, Africa, and the equatorial belt do not. Russia gave it up in 2011. Brazil dropped it in 2019. The European Union has been talking about ending it since 2018.

The transition dates don't line up

This is the part that breaks calendars. The US "springs forward" on the second Sunday of March; Europe does it on the last Sunday of March. So for two weeks every spring, London and New York are four hours apart instead of five. Your 3 PM London / 10 AM NYC meeting? It's now 2 PM London / 10 AM NYC. Whoever set the recurring event on a US time zone wins; whoever anchored on London is suddenly an hour off.

How to not get burned

• Anchor recurring meetings on UTC if everyone agrees, or on the city of the person leading the meeting.
• Re-confirm the week before any DST transition, especially in March and November.
• Use a converter that handles DST automatically — like, ahem, this one. The IANA database is updated whenever a country changes its rules.

Will it ever end?

Probably, eventually, in some places. Until then: assume DST will surprise you at least once a year, and build a habit of double-checking March and November invites.