Arizona's Year-Round MST: The Basics
Clocks in the Sonoran Desert never spring forward. While most of the United States advances an hour each March, Arizona holds steady on Mountain Standard Time (UTC-7) all year.
From March to November, that puts Phoenix, Tucson, Mesa, Chandler, Gilbert, Glendale, and Scottsdale on the same clock reading as California, Oregon, and Washington. But the state is not on Pacific Time. Those coastal states switch to Pacific Daylight Time (UTC-7). Arizona stays on Mountain Standard Time. Same offset, different zone name.
From November to March, Arizona matches the rest of the Mountain Time zone. Denver, Salt Lake City, and Albuquerque all read the same time.
The number that never changes: Arizona is always UTC-7.
Why does Arizona stay on standard time while the rest of Mountain Time springs forward?
The state legislature made a climate-driven calculation in 1968. Arizona exempted itself from daylight saving time under the authority of the Uniform Time Act of 1966, which lets states opt out by passing a state statute.
That statute is Arizona Revised Statutes §1-242. It says Arizona will not observe daylight saving time. The law has not changed since.
The argument legislators heard then is the same one that holds now. An extra hour of evening daylight in summer does not save energy in the desert. It burns more.
Does daylight saving time actually increase energy use in the desert?
The standard case for DST is that it shifts daylight to the evening, cutting artificial lighting and saving electricity. That logic works in temperate climates. It fails in the Sonoran Desert.
Summer daytime temperatures in Phoenix routinely exceed 105 °F. People do not linger outdoors in the late afternoon. They stay inside and run air conditioning. An extra hour of evening daylight means an extra hour of cooling load. The sun sets later, houses stay hotter longer, and air conditioners run harder.
State legislators in 1968 saw that DST would increase, not decrease, energy consumption. They voted to stay on standard time permanently.
The numbers back them up. On the June solstice in Phoenix, the sun rises at 05:18 and sets at 19:40. That is 14 hours 22 minutes of daylight. The hottest part of the day arrives after noon. Extending daylight into the evening would push cooling demand deeper into the day.
Arizona made a practical choice based on climate, not tradition.
Why does part of Arizona follow DST while the rest does not?
Two sovereign nations inside Arizona do not follow the state's rule.
The Navajo Nation observes DST. This semi-autonomous territory spans northeastern Arizona, southeastern Utah, and northwestern New Mexico. It follows the same DST schedule as the rest of the United States. Clocks change in March and November.
The Hopi Reservation is entirely surrounded by the Navajo Nation. It does not observe DST. It follows Arizona's year-round MST.
Mapmakers call this a DST doughnut. The doughnut hole is the Hopi Reservation. The doughnut itself is the Navajo Nation. Both sit inside Arizona, which does not observe DST. A 30-minute drive in northeastern Arizona can cross three time-keeping zones: Arizona standard, Navajo DST, and Hopi standard.
What Arizona Time Means in Summer (Matching Pacific)
When someone says "Arizona is on Pacific Time in summer," they are technically wrong but practically correct.
From the second Sunday in March to the first Sunday in November, the clock in the Valley of the Sun reads the same as Los Angeles and Seattle. But the time zone names differ:
- Los Angeles: Pacific Daylight Time (PDT), UTC-7
- Phoenix: Mountain Standard Time (MST), UTC-7
Both show 14:00. One is in daylight time, the other in standard time. The offset matches, so the confusion is understandable.
The problem arises when someone schedules a "2 PM Pacific" call with the state's capital in July. Pacific Time is PDT, which is UTC-7. The city is MST, also UTC-7. The call works. But if the same person schedules a "2 PM Mountain" call with the same city in July, they likely mean MDT (UTC-6). The city is UTC-7. That call is an hour off.
The correct way to schedule with Arizona: use "Arizona time" or "MST" and specify the UTC offset. Never use "Mountain Time" without checking the date.
How Arizona's fixed clock scrambles TV, meetings, and flights
Television and Primetime
A constant time zone shifts primetime television by season. In winter, when the rest of the Mountain zone is on MST, Arizona matches it. Primetime runs 18:00 to 21:00. In summer, the rest of the Mountain zone switches to MDT (UTC-6), but Arizona stays on MST (UTC-7). Primetime effectively shifts to 19:00 to 22:00, matching Pacific.
Live events like Monday Night Football start at 18:15 in Arizona in winter and 19:15 in summer.
Business and Meetings
Businesses in the Grand Canyon State operate on a single time zone all year. That simplifies internal scheduling. External scheduling is the headache.
In winter, the state's largest city is two hours behind New York. A 10:00 AM meeting there is noon in New York. In summer, it is three hours behind New York. That same 10:00 AM meeting is 13:00 in New York.
Companies with offices in both the Arizona capital and Denver must manage a one-hour difference in summer. Denver is on MDT (UTC-6). The Arizona office is on MST (UTC-7). A 9:00 AM meeting in Denver is 8:00 AM in the desert office.
Travel
Travelers flying into Sky Harbor need to reset their expectations. If you fly from Chicago in July, Chicago is on Central Daylight Time (UTC-5). The destination is on MST (UTC-7). You lose two hours. If you fly from Denver in July, Denver is on MDT (UTC-6). The destination is on MST (UTC-7). You lose one hour even though both cities sit in the Mountain zone.
The next change coming for the rest of the Mountain zone is Sunday 07 November 2027 at 02:00 local, when clocks fall back from MDT to MST. Arizona will not change. If you are in Denver or Calgary that morning, you gain an hour. If you are in the desert city, your clock stays the same. That is the point: Arizona never changes.