Does Arizona observe daylight saving time?
No — which makes Phoenix the hardest US city to schedule against, because it changes which coast it matches without ever changing its clock.
The short answer
No. Arizona stays on MST (UTC−7) all year. The one exception is the Navajo Nation, which does observe it.
But Phoenix meetings still move twice a year — because everyone else changes. Arizona is 2 hours ahead of New York in winter and 3 hours ahead in summer.
Why not
Arizona observed daylight saving in 1967, disliked it, and opted out permanently in 1968 under the provision in the Uniform Time Act that lets a state exempt itself.
The argument was heat. Phoenix summers regularly exceed 40 °C, and evenings are the only tolerable part of the day. Shifting an hour of sunlight from the early morning into the evening makes the hot part of the day longer, pushes cooling demand up rather than down, and delays the point at which it is bearable to go outside.
Daylight saving is meant to move usable daylight into waking hours. In a desert climate, the late-afternoon hour it adds is not usable.
The trap: Arizona still moves relative to you
This is the part that catches people, and it is why Phoenix is genuinely the hardest US city to schedule against.
Arizona's clock is fixed. Everyone else's is not. So Arizona's relationship to every other US zone changes twice a year:
| Season | Phoenix vs Los Angeles | Phoenix vs Denver | Phoenix vs New York |
|---|---|---|---|
| Winter | 1 hour ahead | same time | 2 hours ahead |
| Summer | same time | 1 hour behind | 3 hours ahead |
In winter Phoenix matches Denver. In summer it matches Los Angeles. Same city, same clock, two different answers.
A recurring call with a Phoenix colleague will move by an hour in March and again in November, and from Phoenix's point of view nothing happened at all.
"MST" means two different things
Arizona is on Mountain Standard Time year-round. Denver is on Mountain Standard Time in winter and Mountain Daylight Time in summer.
So "MST" is always correct for Phoenix and correct for Denver only half the year. Two cities, the same abbreviation, different behaviour — which is a compact demonstration of why abbreviations are a poor identifier and city names are not.
Write "Phoenix".
The Navajo Nation
The Navajo Nation observes daylight saving and extends into Arizona. The Hopi Reservation, which sits inside the Navajo Nation, does not.
The time zone database handles this with distinct zone identifiers rather than treating Arizona as uniform — another reason to resolve times against a zone name rather than a state.
What to do about it
Put both local times in any recurring invitation, and re-check anything involving Phoenix at the two US transition dates — 2026-03-08 and 2026-11-01 this year.
Related: Which US states don't observe daylight saving time? · Arizona doesn't change its clocks and it wrecks my calendar
Timezone: World Clock Widget
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Figures on this page are computed from the IANA time zone database. Last generated 2026-08-18.