The Two States That Stay on Standard Time All Year
The list is two names long and has not changed since the late 1960s. Arizona keeps Mountain Standard Time (MST) year-round. Hawaii stays on Hawaii Standard Time (HST). From March to November, the Grand Canyon State matches Pacific Time (UTC-7), and the islands fall one hour further behind the West Coast than they do in winter.
Indiana came close. Parts of the state ignored DST for decades, but the whole state adopted it in 2006. That left the two holdouts untouched.
| State | Standard Time Zone | Year Opted Out | Current Offset (Year-Round) |
|---|---|---|---|
| Arizona | Mountain (MST) | 1968 | UTC-7 |
| Hawaii | Hawaii (HST) | 1967 | UTC-10 |
Why Does Arizona Ignore Daylight Saving?
Heat, not sunlight, drives the decision. The state exempted itself permanently in 1968 after a brief trial under the 1966 Uniform Time Act. A desert summer already strains air conditioning. An extra hour of afternoon sun forces homes to cool harder during the hottest stretch and wastes the cooler morning hours on an earlier alarm.
The practical result: Phoenix reads the same as Los Angeles from March to November (UTC-7) and matches Denver from November to March. Denver switches to UTC-7 in winter. The Grand Canyon State sits there all year. Call Phoenix in July assuming Mountain Time and you will be an hour off.
Does Any Part of Arizona Follow DST?
Yes. The Navajo Nation observes DST, even inside the state. The nation spans Utah and New Mexico, both of which change clocks, and it runs on one internal schedule. The portion inside Arizona springs forward with the rest of the country while the surrounding state does not.
The Hopi Reservation: Standard Time Inside the Navajo Nation
Inside the Navajo Nation sits the Hopi Reservation. It does not observe DST. It keeps Arizona standard time all year. The result is one of the strangest time maps in the country: a reservation on DST surrounding a reservation on standard time, inside a state that ignores DST entirely. Drive through northeastern Arizona in July and you can cross three different time practices in under an hour.
Why Does Hawaii Skip Daylight Saving?
Latitude. At 21° north, the difference between a summer day and a winter day is less than two hours. Shifting clocks forward buys almost no extra evening light. The disruption is not worth it. Hawaii opted out in 1967.
Hawaii Standard Time stays at UTC-10 all year. The gap to the mainland shifts with the seasons. In January Honolulu is two hours behind Los Angeles and five behind New York. In July it is three and six.
US Territories That Don’t Observe DST
No US territory observes DST. The five inhabited territories stay on standard time year-round:
| Territory | Standard Time Zone | Offset (Year-Round) |
|---|---|---|
| Puerto Rico | Atlantic (AST) | UTC-4 |
| US Virgin Islands | Atlantic (AST) | UTC-4 |
| Guam | Chamorro (ChST) | UTC+10 |
| Northern Mariana Islands | Chamorro (ChST) | UTC+10 |
| American Samoa | Samoa (SST) | UTC-11 |
All five sit at low latitudes where seasonal daylight varies little. Puerto Rico matches Eastern Daylight Time in summer and sits one hour ahead of Eastern Standard Time in winter. See the full guide to US Territories Time Explained for details.
Could Other States Opt Out?
Yes. Any state can drop DST and stay on standard time permanently. The Uniform Time Act of 1966 permits that. What states cannot do is adopt permanent DST without an act of Congress. That is why the Sunshine Protection Act keeps reappearing: it would let states keep DST year-round.
Several states have passed trigger laws that would activate permanent DST if Congress authorizes it. As of October 2026, none have taken effect. For the current DST schedule, see When Does Daylight Saving Time Start and End?.