Mountain Time Zone

In Canada and the United States, this time zone is generically called Mountain Time (MT). Specifically, it is Mountain Standard Time (MST) when observing standard time, and Mountain Daylight Time (MDT) when observing daylight saving time. The term refers to the Rocky Mountains.

Baja California Sur, Sinaloa, and Sonora in Mexico, and most of Arizona in the United States, do not observe daylight saving time (DST), and during the spring, summer, and autumn months they are on the same time as Pacific Daylight Time. The Canadian province of British Columbia and Yukon Territory observe permanent daylight saving time in the Pacific Time Zone, which is equivalent to year-round Mountain Standard Time.

The largest city in the Mountain Time Zone is Phoenix, Arizona; the Phoenix metropolitan area is the largest metropolitan area in the zone. The largest city that observes daylight saving time is Juárez, Chihuahua, Mexico.

The clock time in this zone is based on the mean solar time at the 105th meridian west of the Greenwich Observatory. In the United States, the exact specification for the location of time zones and the dividing lines between zones is set forth in the Code of Federal Regulations at 49 CFR 71.

Canada

One territory is fully contained in the Mountain Time Zone:

• Yukon (no DST)

One province is split between the Mountain Time Zone and the Central Time Zone:

• British Columbia – all except Regional District of East Kootenay, Town of Golden, and Columbia-Shuswap Regional District Area A

One territory is split between the Mountain Time Zone, the Central Time Zone, and the Eastern Time Zone:

• Nunavut – Kitikmeot Region

On September 24, 2020, Yukon switched to the Mountain Standard Time year-round. Previously, the territory had used the Pacific Time Zone with daylight saving time: UTC−8 in winter and UTC−7 in summer.

On March 8, 2026, most of British Columbia in the Pacific Time Zone adopted UTC−7 year-round but continue to call their time zone "Pacific Time" with a new abbreviation of "PCT".

Alberta observed Mountain Time with daylight saving until 2026, when it switched to Central Standard Time (UTC−06:00) year-round. The western half of Saskatchewan observed Mountain Time without daylight saving until 1972 when it joined the rest of the province in Central Standard Time.

Following Alberta's switch to Central Standard Time year-round, on August 14, 2026, the Regional District of East Kootenay in southeastern BC also switched to Central Standard Time year-round from Mountain Time with daylight saving to maintain its alignment with Alberta. The Town of Golden and Columbia-Shuswap Regional District, which were also previously on Mountain Time with daylight saving time, originally adopted permanent standard time on September 1, 2026, planning to sync the localities with the rest of BC besides the Regional District of East Kootenay by moving an hour back on November 1, 2026. However, on September 22, 2026, this decision was reversed and the two municipalities opted to adopt Central Standard Time year-round, retaining continuity with Alberta and East Kootenay.

Similarly, the Northwest Territories observed Mountain Time with daylight saving until 2026 before switching to Central Standard Time year-round on August 21, 2026.