What is the difference between PST and PDT?
PST and PDT are the winter and summer settings of one clock — Pacific Time — not two different time zones. Pacific Standard Time (PST) is the region's standard time, the offset it keeps through the winter half of the year: eight hours behind Coordinated Universal Time, written UTC−8.14 Pacific Daylight Time (PDT) is the same zone advanced by one hour for the summer half, at UTC−7. The two are exactly one hour apart, and a place on Pacific Time is always on one or the other — never both, never neither.2
United States federal law names and fixes the standard half of the pair directly. The statute that lists the country's zones assigns Pacific standard time as "Coordinated Universal Time retarded by 8 hours," and a companion section designates that zone "Pacific standard time."16 PDT is not defined separately; it is simply PST with daylight saving time applied, an across-the-board one-hour advance during the warmer months.
"PT," or Pacific Time, is the umbrella label for the zone regardless of season. It resolves to PST in winter and PDT in summer, so it is the safe choice when a date could fall on either side of a clock change — a broadcast schedule, a recurring meeting, a software setting. The same three-way pattern of standard, daylight, and umbrella labels repeats across the United States: Eastern Time splits into EST and EDT, Central into CST and CDT, Mountain into MST and MDT.
When is it PST, and when is it PDT?
Pacific Time is on PDT during daylight saving time and on PST the rest of the year. In the United States, daylight saving time runs from 02:00 local time on the second Sunday in March to 02:00 local time on the first Sunday in November.3 At the March transition Pacific clocks spring forward from PST to PDT; at the November transition they fall back from PDT to PST. In 2026 that window runs from 8 March to 1 November — so for about 238 days of the year the correct label is PDT, and only the remaining stretch of winter is genuinely PST.3
These dates are set by statute, not by season or weather. The Energy Policy Act of 2005 amended the federal Uniform Time Act, striking the old "first Sunday of April" start and "last Sunday of October" end and replacing them with the current second-Sunday-of-March and first-Sunday-of-November dates, effective from March 2007.5 Because the rule is federal, every part of the country that observes daylight saving — Pacific, Mountain, Central, and Eastern alike — changes on the same two Sundays. The mechanics of the spring-forward and fall-back transitions, and the history behind them, are covered on the daylight saving time page.
How can I tell whether it's PST or PDT right now?
The quickest rule of thumb: if the date is between the second Sunday in March and the first Sunday in November, the Pacific coast is on PDT (UTC−7); otherwise it is on PST (UTC−8). As of mid-2026, for example, the region is on PDT. The reliable test, rather than the rule of thumb, is the live UTC offset: a Pacific clock reading seven hours behind UTC is on PDT, and one reading eight hours behind is on PST.2
For an exact answer at any instant — including the awkward hours right around a transition — read the current offset from a clock that tracks it, rather than guessing from the calendar. The site's time-zone converter shows the live Pacific time and its current offset against UTC and any other zone, which settles the PST-or-PDT question without arithmetic. A fuller treatment of the named zone itself lives on the Pacific Time reference page.
PST vs PDT at a glance
| Label | Full name | UTC offset | When it applies | IANA zone |
|---|---|---|---|---|
| PST | Pacific Standard Time | UTC−8 |
Winter — first Sunday Nov to second Sunday Mar | America/Los_Angeles |
| PDT | Pacific Daylight Time | UTC−7 |
Summer — second Sunday Mar to first Sunday Nov | America/Los_Angeles |
| PT | Pacific Time (umbrella) | UTC−8 or UTC−7 |
Year-round — whichever of PST/PDT is in force | America/Los_Angeles |
Why people write "PST" when they mean "PDT"
"PST" is widely used as a generic stand-in for Pacific Time all year, including the eight months when the zone is actually on PDT. A meeting set for "9 a.m. PST" in July is, strictly, an hour off from "9 a.m. PDT," because PST is UTC−8 and the clock in California in July reads UTC−7.2 The error usually causes no harm — most people read "PST" as "Pacific Time" and apply the current offset anyway — but it is wrong, and around the March and November switchovers the ambiguity can shift a scheduled time by a full hour.
The clean habit is to write "PT" whenever the season is uncertain or the event recurs across a clock change, and to reserve "PST" and "PDT" for moments that genuinely fall in winter and summer respectively. The same slip happens in every United States zone — "EST" stood in for Eastern Time year-round long before "PST" did — which is why the umbrella forms (PT, ET, CT, MT) exist at all. The broader set of these labels is catalogued in the time-zone abbreviations reference.
Which places use Pacific Time?
Pacific Time covers the west coast of North America and a band of the interior west. In the United States it is the civil time of California, Washington, and Oregon, most of Nevada, and the Idaho panhandle — cities including Los Angeles, San Francisco, San Diego, San Jose, Seattle, Portland, Las Vegas, and Reno. All of them keep the same schedule, switching between PST and PDT on the federal dates, and all share the IANA zone identifier America/Los_Angeles.2
The zone extends beyond the United States. The Canadian province of British Columbia — Vancouver and Victoria — keeps Pacific Time under the identifier America/Vancouver, and Mexico's Baja California state, including Tijuana, keeps it as America/Tijuana. Both observe the same PST/PDT changeovers as the United States: British Columbia by its own provincial rule, and Baja California under an exception that keeps Mexico's northern border aligned with United States clocks for cross-border commerce, even though most of Mexico abolished daylight saving in 2022.2
Frequently asked questions
Is it PST or PDT in summer?
In summer it is PDT (Pacific Daylight Time), UTC−7. The Pacific coast is on PDT from the second Sunday in March to the first Sunday in November, which covers all of the meteorological summer.3
How many hours behind UTC is Pacific Time?
Pacific standard time is eight hours behind Coordinated Universal Time (UTC−8); Pacific daylight time is seven hours behind (UTC−7). The difference is the one-hour daylight saving advance applied in the summer half of the year.12
Is PST the same as PT?
No. "PT" (Pacific Time) is the umbrella that means whichever of PST or PDT is currently in force, while "PST" specifically means the winter standard time at UTC−8. For most of the year PT actually equals PDT, not PST.4
Does all of California use the same Pacific Time?
Yes. The entire state of California observes Pacific Time and switches between PST and PDT on the same federal dates, sharing the IANA zone America/Los_Angeles with Washington, Oregon, and Nevada.2
Footnotes
- 1. 15 U.S. Code § 261 — Zones for standard time; interstate or foreign commerce , Office of the Law Revision Counsel, U.S. House of Representatives (Legal Information Institute edition) — accessed 2026-06-06.
- 2. tz database — northamerica file (Rule US; Zone America/Los_Angeles) , Internet Assigned Numbers Authority (Time Zone Database) — accessed 2026-06-06.
- 3. Daylight Saving Time (DST) , National Institute of Standards and Technology, Time and Frequency Division — accessed 2026-06-06.
- 4. U.S. Time Zones (Astronomical Information Center) , U.S. Naval Observatory — accessed 2026-06-06.
- 5. Energy Policy Act of 2005, Public Law 109-58, § 110 (amending the Uniform Time Act of 1966) , U.S. Government Publishing Office (2005) — accessed 2026-06-06.
- 6. 15 U.S. Code § 263 — Designation of zones , Office of the Law Revision Counsel, U.S. House of Representatives (Legal Information Institute edition) — accessed 2026-06-06.