Time zones. Blecch. It's bad enough that we have to remember that there are nine standard time zones in the United States and its territories. Then there's that [horrid] system we call Daylight Saving Time, which effectively adds seven more time zones.
Most of Arizona is the same way, but there are exceptions.
How to Determine What Time It Is in the United States
All times can be easily calculated since they are based on UTC (Universal Time Coordinated) which is used worldwide. UTC never changes; it is not a time zone. Regional time zones make adjustments to the relationship of their times to UTC.
For example, California is 8 hours behind UTC during Standard Time and 7 hours behind UTC during Daylight Saving. UTC never changes, only the local time changes. Arizona is 7 hours behind UTC, or UTC-7.
You can use this time zone converter to see what time it is in any city compared to another city.
First Sunday in November through Second Sunday in March
All U.S. states are on Standard Time. The time in Phoenix is one hour later than it is in California, for example, Phoenix is two hours earlier than it is in New York. Arizona is three hours later than Hawaii.
During this time, Standard Time, Arizona's local time is the same as New Mexico, Colorado, Utah, Wyoming and Montana, all of which are also UTC-7.
Second Sunday in March through First Sunday in November
All U.S. states except Arizona and Hawaii observe Daylight Saving Time (DST) by setting their clocks ahead one hour.
Phoenix is the same as it is in California, for example, Phoenix is three hours earlier than it is is New York.
Because neither Hawaii or Arizona observe DST, Arizona is always three hours ahead of Hawaii (UTC-7 vs. UTC-10). During Daylight Saving Time, Arizona's local time is the same as California, Nevada, Oregon, and Washington., all of which are UTC-7.
Exceptions to MST in Arizona
The Navajo Nation in Northern Arizona DOES observe Daylight Saving Time. That means that for half the year there are parts of Arizona that are on different times. Even worse, I stayed at a resort on Navajo land that actually opted out of Daylight Saving Time. It was so confusing! When I asked about it I was told that since most of their guests were expecting them to use Arizona's time zone they decided to stick with Mountain Standard Time.
Myth: Arizona Changes to Pacific Time for Half the Year
This is a common myth. Arizona doesn't change time zones, ever. It just so happens that MST and PDT, as you can see on the chart above, are on the same time, UTC-7, for half the year.
Tip: All the major cities in Arizona, including Tucson, Mesa, Scottsdale, Glendale and Flagstaff, are always the same time as Phoenix.