EST to MST and MST to EST converter

Arizona: Mountain Standard Time all year

Arizona has not used daylight saving time since 1968, apart from the Navajo Nation in the northeast of the state. While the rest of the country springs forward in March, Phoenix and Tucson stay on MST (UTC−7), which puts them on the same clock as Los Angeles from March to November and the same as Denver from November to March.

• Winter (early November to mid-March): Arizona is 2 hours behind Eastern and matches Denver.
• Summer (mid-March to early November): Arizona is 3 hours behind Eastern and matches Pacific Time.

So a meeting invite that says “MST” in July is ambiguous: for Arizona it is correct, but Denver is actually on MDT then. Naming the city avoids the mix-up.

Where Mountain Time is used

Colorado, Utah, New Mexico, Wyoming and Montana are entirely on Mountain Time, as is southern Idaho including Boise. It also covers the western edges of Kansas, Nebraska and the Dakotas, El Paso in Texas, and most of Malheur County in Oregon.

Markets and TV

The stock market opens at 9:30 AM Eastern, which is 7:30 AM in Denver, and 6:30 AM in Phoenix during the summer. Network prime time in the Mountain zone usually runs 7–10 PM, an hour earlier by the clock than on the East Coast.