Daylight Saving Checker

In short Whether a place changes its clocks, and exactly when, is a legislative fact rather than an astronomical one, and it changes more often than people expect — countries adopt daylight saving, abandon it, or shift their dates, and several have done so in the last few years. This page does not carry a list of those dates. It asks your browser for the zone's offset at points through the year and bisects wherever the offset changes, which locates each transition to the minute using whatever IANA data your browser currently holds. Two things usually surprise people. The first is how few zones do this at all: of the several hundred a browser knows, roughly seven in ten have no transitions in a year, so a constant offset is the normal case worldwide and daylight saving is the regional exception. The second is what a transition actually does. Going forward, an hour is deleted — if the clocks jump from 01:00 to 02:00 then no clock in that zone ever reads 01:30 that day, and a wall time inside the gap refers to no instant at all. Going back, an hour is duplicated, so 01:30 happens twice and the two are separate instants an hour apart. Those two hours are where log timestamps collide, shift rotas double up and scheduled jobs run twice or not at all.