Pst pdt

How it works

Pacific Time is a civil zone on the west of North America. When the region is on standard time, clocks read PST and sit eight hours behind Coordinated Universal Time. When the region is on daylight time, clocks read PDT and sit seven hours behind. The pair is the whole story: you never run both offsets in the same town at the same moment.

In the United States the switch follows a fixed federal rule. Clocks spring forward on the second Sunday in March, at 02:00 local time, and fall back on the first Sunday in November, at 02:00 local time. On the March morning, 01:59 is followed by 03:00, and that hour is PDT. On the November morning, 01:00 to 01:59 happens twice: first as PDT, then as PST.

Those Sundays move from year to year because they are weekdays, not month dates. In 2026 the spring change is 8 March and the autumn change is 1 November. In 2027 the spring change is 14 March and the autumn change is 7 November. The labels PST and PDT are how a clock tells you which side of that seam you are on.

Writing only “Pacific Time” is safer in a letter that must survive the seam. Writing “17:00 PST” in July is a mismatch: July is daylight time on this zone, so the honest label is PDT. Software that stores a timestamp should store an offset or a named zone such as America/Los_Angeles, not a frozen three-letter tag.

The pair on a clock face

Think of PST and PDT as two hats for the same head. The geography does not move. Los Angeles, Seattle, and Vancouver do not jump to a new zone in March; they change which offset that zone uses. A meeting booked as “10:00 Pacific Time” stays at 10:00 local through the year. A meeting booked as “18:00 UTC” stays fixed against UTC and therefore slides by one local hour when the pair swaps.

If you compare Pacific Time with a zone that does not change, the gap is not constant: Against UTC, the gap is eight hours on PST and seven hours on PDT. Against a year-round UTC+9 clock, the gap is seventeen hours on PST and sixteen hours on PDT.

Against another US zone that also changes on the same Sundays, the gap between them usually stays one or two hours all year. Arizona is the usual exception people meet in the same country: most of the state stays on Mountain Standard Time and does not spring forward, so the gap between Phoenix and Los Angeles shrinks and grows with the Pacific pair. The Pacific labels themselves are not at fault; the other clock simply does not join the dance.

When a label is the wrong one

Three-letter time abbreviations are overloaded. IST can mean Irish Standard Time or India Standard Time. CST can mean Central Standard Time or China Standard Time. PST is a little cleaner in ordinary US use, but it still fails if you need a historical offset, a ship at sea, or a server that must not guess. Prefer the city zone name when a program has to convert.

For people, the practical test is local noon. If Pacific clocks say 12:00 and UTC says 20:00, you are on PST. If Pacific clocks say 12:00 and UTC says 19:00, you are on PDT. You do not need to memorize the March and November Sundays to read a pair of clocks that are both honest about their offset.

PST and PDT are not neighboring towns. They are the same town in a winter coat and a summer coat, and only one coat is on the hook at a time.