While most of the United States dutifully changes its clocks twice a year, Arizona just... doesn't. It's one of only two states (along with Hawaii) that stays on standard time year-round. The reason comes down to one thing Arizona has in abundance: heat.
The short answer: it's the heat
Daylight Saving Time shifts an hour of daylight from the morning into the evening. In most places, that extra evening daylight is a perk - more usable light after work.
In Arizona, it's the opposite of a perk. In the desert summer, an extra hour of intense evening sunlight means another hour of brutal heat when residents most want the sun to go down. By staying on standard time, Arizona keeps the sun setting earlier, giving people cooler, darker evenings. Skipping DST also means less air-conditioning load during those peak evening hours.
How Arizona is allowed to opt out
Under the US Uniform Time Act of 1966, states are required to follow federal DST rules unless they pass a law exempting themselves. States can't invent their own DST schedule, but they can choose to stay on standard time year-round.
Arizona took that exemption in 1968 and has stuck with it ever since. Hawaii made the same choice for different reasons - being near the equator, its daylight barely varies across the year, so DST offers little benefit.
The Navajo Nation exception
Here's the twist that trips people up: the Navajo Nation, which sits in northeastern Arizona, does observe Daylight Saving Time. The Navajo Nation also extends into Utah and New Mexico (which both observe DST), so it follows DST to stay internally consistent across state lines.
And inside the Navajo Nation sits the Hopi Reservation, which - like the rest of Arizona - does not observe DST. The result is a famous geographic oddity: a series of nested zones where the clock effectively changes as you drive in and out, even though you never cross a state line.
What this means for Arizona's time zone in practice
Arizona is on Mountain Standard Time (MST), UTC−7, all year. Here's the practical effect:
| Time of year | Arizona offset | Same clock as |
|---|---|---|
| Winter (standard time) | UTC−7 | Denver (Mountain) |
| Summer (daylight time) | UTC−7 | Los Angeles (Pacific) |
During US winter, Arizona matches the rest of the Mountain Time zone. During US summer, the rest of Mountain Time springs forward to UTC−6, but Arizona stays at UTC−7. In summer, Arizona effectively keeps the same clock time as Pacific Time, not Mountain Time.
That seasonal flip is exactly why people scheduling calls with Phoenix get confused - for half the year Arizona "matches" Denver, and for the other half it "matches" Los Angeles.
The bottom line
Arizona skips Daylight Saving Time because, in a desert, more evening sunlight is a burden, not a benefit. The state legally exempted itself in 1968 and has stayed on permanent Mountain Standard Time since - with the Navajo Nation as the notable exception. The practical upshot: Arizona's clock never changes, but its relationship to its neighbors does, flipping between matching Denver in winter and Los Angeles in summer.