Time Zones

Pacific Daylight Time (PDT)

UTC offset: -07:00
Standard offset: -08:00 (PST)
IANA identifier: America/Los_Angeles
Abbreviation: PDT
Population: approximately 55 million
DST period: Second Sunday in March to first Sunday in November

Pacific Daylight Time moves the West Coast forward one hour from PST each spring, putting clocks at UTC-07:00. The shift happens at 2:00 a.m. on the second Sunday in March (clocks jump to 3:00 a.m.) and reverses at 2:00 a.m. on the first Sunday in November (clocks fall back to 1:00 a.m.). For roughly eight months of the year, PDT is the active offset for most of the Pacific Time Zone.

During PDT, the West Coast is only two hours behind Eastern Daylight Time (EDT) rather than three. Wait, no. The gap stays at three hours regardless. Both zones shift simultaneously, so the ET/PT difference never changes. But the gap to Arizona (which doesn't observe DST) does change: during PDT, Arizona and the Pacific coast share the same clock. During PST, Arizona is one hour ahead.

Coverage

PDT applies to the same territories as PST during the summer months:

  • United States: California, Oregon, Washington, Nevada, northern Idaho
  • Canada: British Columbia (the Yukon stopped observing DST in 2020, staying on permanent -07:00 year-round)
  • Mexico: Baja California (the northern peninsula, including Tijuana and Mexicali)

The tech corridor from San Jose through San Francisco to Seattle runs entirely on Pacific Daylight Time during the majority of the business year. Product launches, earnings calls, market opens, and startup demo days all happen on PDT clocks from March to November.

The Tech Industry Clock

Silicon Valley operates on PDT for more of the year than it operates on PST. This matters because the global tech calendar is built around it. Apple's WWDC keynotes, Google I/O, Meta earnings calls, and Amazon product announcements are scheduled in PT. When tech journalists write "10 a.m. PT," they usually mean PDT during the eight months it's active.

The West Coast market opening is relevant too. The NYSE and NASDAQ open at 9:30 a.m. ET, which is 6:30 a.m. PDT. West Coast traders and tech company executives who care about their stock price must be functional before dawn Pacific time. This is why so many Silicon Valley executives are aggressive about early morning routines. It's not just productivity culture; it's the three-hour market gap.

Entertainment Industry

Los Angeles controls an outsized share of global media production. During PDT, the primetime TV schedule on the Pacific coast runs 8:00-11:00 p.m. PDT. The Oscars, Grammys, and Emmys broadcast live from LA, starting at 5:00 p.m. PDT (which is 8:00 p.m. EDT, the compromise that satisfies neither coast perfectly).

Film production call times, post-production deadlines, and studio executive meetings all run on the PDT clock during shooting seasons. The phrase "Hollywood time" in global entertainment essentially means Pacific Time.

The Arizona Problem

Arizona doesn't observe DST (with the exception of the Navajo Nation, which does). So during PDT, Arizona and the Pacific coast are synchronized at -07:00. During PST, Arizona is one hour ahead at -07:00 while the coast is at -08:00. This creates semi-annual confusion for anyone scheduling cross-border meetings between Phoenix and Los Angeles.

Practical result: for about eight months per year, Phoenix and LA are on the same time. For four months, Phoenix is an hour ahead. Software calendars handle this correctly if you set locations properly, but phone calls arranged casually often hit this trap.

Permanent DST Proposals

California, Washington, and Oregon have all passed legislation or ballot measures favoring permanent PDT. The idea: stay at -07:00 year-round, gaining evening light in winter at the cost of darker mornings.

The problem: federal law (the Uniform Time Act of 1966) doesn't allow permanent DST. It allows permanent standard time (which is how Arizona opts out). The Sunshine Protection Act passed the US Senate in 2022 but stalled in the House. Without federal action, Pacific states cannot unilaterally adopt permanent PDT.

If it ever happened, the practical consequences for Seattle would be dramatic: sunrise on the winter solstice would not occur until approximately 8:55 a.m. Portland would be similar. LA would be less affected (sunrise around 7:58 a.m. at the solstice).

International Context

During PDT:

  • London (BST): 8 hours ahead
  • Tokyo: 16 hours ahead
  • Sydney (AEST): 17 hours ahead
  • New York (EDT): 3 hours ahead
  • Denver (MDT): 1 hour ahead
  • Arizona (MST, no DST): same time
  • Honolulu (HST, no DST): 3 hours behind

The 8-hour gap to London during mutual summer time (both PDT and BST active) is the most manageable transatlantic window for West Coast workers. A 9 a.m. PDT call is 5 p.m. in London, catching the end of the British workday.

The Brief Transition Anomalies

Because DST start/end dates differ between countries, there are brief periods when the usual time gaps shift. The US switches to DST in March; the UK switches to BST in late March. For those 2-3 weeks, the US-UK gap is 7 hours instead of 8. Similarly, when the US falls back in November but the UK hasn't yet, the gap is temporarily 7 hours. These windows trip up international scheduling for a few weeks each year.

Scheduling Strategies

West Coast professionals develop coping mechanisms for the 3-hour Eastern gap:

  • Many start work at 6:00-7:00 a.m. PDT to overlap with ET morning
  • Cross-Pacific calls with Asia happen 5:00-8:00 p.m. PDT (morning in Tokyo/Singapore)
  • Internal meetings cluster 10:00 a.m.-2:00 p.m. PDT (1:00-5:00 p.m. EDT), the "golden window"
  • Friday afternoons on the West Coast are often meeting-free because the East Coast has already left

Technical Identifiers

  • America/Los_Angeles (IANA canonical, US)
  • America/Vancouver (IANA, Canada)
  • America/Tijuana (IANA, Mexico)
  • PDT (Pacific Daylight Time)
  • Windows: "Pacific Standard Time" (covers both PST and PDT)
  • Military/aviation: U ("Uniform") for UTC-08:00 base, but PDT = T ("Tango") for UTC-07:00

Quick Reference

Attribute Value
UTC offset -07:00
Active period ~Mar to ~Nov (8 months)
DST transition 2nd Sunday March / 1st Sunday November
IANA zone America/Los_Angeles
Population ~55 million
Key cities LA, SF, Seattle, Vancouver, Tijuana
Gap to ET 3 hours (always)
Gap to London (BST) 8 hours
Gap to Tokyo 16 hours