What is the name of the time zone used in Arizona year-round?

The name of the time zone used in Arizona year-round is Mountain Standard Time (MST). Most of Arizona stays at UTC−7 throughout the calendar year and does not move its clocks forward for daylight saving time.

Arizona’s year-round schedule dates to 1968, when the state legislature approved an exemption from daylight saving time. The policy was influenced partly by the state’s hot desert climate: extending evening daylight can mean more hours of air-conditioning use during the hottest part of the day.

There is one important geographic exception. The Navajo Nation, which extends across Arizona, New Mexico, and Utah, observes daylight saving time. The Hopi Reservation, surrounded by the Navajo Nation within Arizona, does not. Trivia questions generally mean most of the state when they describe Arizona as remaining on MST year-round.

A common mix-up is confusing MST with Mountain Daylight Time (MDT). Neighboring states such as Utah and New Mexico switch between those two labels, while Phoenix and most of Arizona remain on MST. As a result, Arizona’s clock can match Pacific time in summer and Mountain time in winter.