Mountain Standard Time (MST) - Time Zone

What Is Mountain Standard Time (MST)?

Mountain Standard Time (MST) is the time zone covering the Rocky Mountain region of North America. It sits seven hours behind Coordinated Universal Time, at a fixed offset of UTC−7.

MST serves the American West from the high peaks of Colorado to the deserts of Arizona and New Mexico. When daylight saving time kicks in, most of the region shifts to Mountain Daylight Time (MDT), which is UTC−6. But Arizona refuses to play along — most of the state stays on MST year-round, creating one of the most confusing time zone situations in the country.

Geographic Coverage

Mountain Standard Time stretches across a huge swath of western North America. Six US states fall entirely within the Mountain Time Zone: Arizona, Colorado, Montana, New Mexico, Utah, and Wyoming. Seven additional states have portions in Mountain Time: Idaho (southern half), Kansas (western counties), Nebraska (western panhandle), North Dakota (southwestern corner), Oregon (small eastern slice), South Dakota (western half), and Texas (El Paso area).

In Canada, Alberta sits fully in the Mountain Time Zone. Parts of British Columbia, the Northwest Territories, and Nunavut also observe Mountain Time. Yukon switched to MST year-round in late 2020. In Mexico, Sonora state uses MST year-round, while northern border cities like Ciudad Juárez follow the US daylight saving schedule.

When compared to neighboring time zones:

• MST is one hour ahead of Pacific Standard Time (UTC−8).

• MST is one hour behind Central Standard Time (UTC−6).

10 Largest Cities in the Mountain Time Zone

Historical Background

Before 1883, there was no such thing as standardized time in America. Every city set clocks to local solar noon, which worked fine until railroads made fast travel possible. A train leaving Pittsburgh might pass through dozens of local times before reaching Chicago. Scheduling became a nightmare.

On November 18, 1883 — "The Day of Two Noons" — railroad companies took matters into their own hands. They divided the continent into four time zones: Eastern, Central, Mountain, and Pacific. At noon, clocks across the country reset to the new standard. Some towns experienced noon twice that day.

The Mountain Time Zone was based on the 105th meridian west, a line of longitude running directly through Denver Union Station. Congress didn't formally adopt railroad time until the Standard Time Act of 1918, which also introduced daylight saving time as a wartime energy measure.

Arizona observed DST briefly in 1967, then opted out the following year. The state decided extra evening sunlight just meant higher air conditioning bills in the desert heat.

Mountain Standard Time vs Mountain Daylight Time

MST and MDT represent two different offsets, and mixing them up causes scheduling headaches:

• Mountain Standard Time (MST): UTC−7, used roughly from early November to mid-March.

• Mountain Daylight Time (MDT): UTC−6, used roughly from mid-March to early November.

The switch happens on the second Sunday of March (clocks spring forward at 2:00 AM to 3:00 AM) and the first Sunday of November (clocks fall back at 2:00 AM to 1:00 AM). In 2025, daylight saving time begins March 9 and ends November 2.

For most of the year, saying "MST" when you mean "MDT" puts you an hour off. During summer, Denver is on MDT (UTC−6), not MST. Phoenix stays on MST year-round, which means Denver and Phoenix match in winter but differ by an hour in summer.

The Arizona Exception

Arizona's relationship with time zones is famously messy. Since 1968, most of Arizona has stayed on MST year-round, making it one of only two US states (along with Hawaii) that don't observe daylight saving time.

The reasoning was practical: summer temperatures regularly exceed 110°F (43°C), and an extra hour of afternoon sunlight just means more air conditioning. State lawmakers figured the supposed energy savings of DST worked in reverse in the desert.

But there's a wrinkle. The Navajo Nation, which spans northeastern Arizona plus parts of New Mexico and Utah, does observe DST to stay synchronized across all three states. And the Hopi Reservation, completely surrounded by the Navajo Nation within Arizona, doesn't observe DST. Drive Arizona State Route 264 from Tuba City eastward during summer, and you'll pass through as many as six time changes in under 100 miles.

This means Phoenix matches Los Angeles during summer (both UTC−7) but matches Denver during winter (both UTC−7, since Denver falls back from MDT). Scheduling calls between Phoenix and other cities requires checking the calendar first.

Practical Uses of Mountain Standard Time

MST shapes daily life across a diverse region:

Energy and Mining: Colorado's oil and gas operations, Wyoming's coal mines, and Utah's extraction industries all run on Mountain Time. Alberta's massive oil sands operations coordinate with markets worldwide from MST/MDT.

Outdoor Recreation: The Mountain Time Zone contains world-class ski resorts (Vail, Park City, Aspen, Big Sky), national parks (Yellowstone, Grand Canyon, Zion, Rocky Mountain), and hiking destinations that draw millions of visitors yearly. All operating hours are local time.

Technology: Denver and Salt Lake City have grown into significant tech hubs. The time zone provides decent overlap with both coasts — 9 AM Mountain is 11 AM Eastern and 8 AM Pacific.

Sports Broadcasting: NFL games kicking off at 1 PM Eastern start at 11 AM Mountain. Sunday Night Football at 8:20 PM Eastern means 6:20 PM for Denver viewers — early enough to wrap up before bedtime.

Cross-Border Commerce: Calgary and Edmonton maintain close business ties with the US Mountain states. El Paso's economy is intertwined with Ciudad Juárez across the border, and both observe the same daylight saving schedule.

Common Confusions and Mistakes

Several errors pop up regularly with Mountain Time:

• Forgetting Arizona's exception: Phoenix doesn't observe DST. From March to November, Arizona is an hour behind Denver despite both being "Mountain Time."

• Mixing up MST and MDT: During summer, most of the zone uses MDT (UTC−6), not MST. Saying "MST" in July puts you an hour off for Denver but is correct for Phoenix.

• Assuming Mountain Time matches Pacific in summer: Arizona (MST) matches California (PDT) during summer — both are UTC−7. But Colorado (MDT) does not match California during summer.

• The Navajo/Hopi confusion: The Navajo Nation observes DST even within Arizona. The Hopi Reservation, surrounded by Navajo land, does not. It's possible to change time zones multiple times driving across northeastern Arizona.

• Ignoring Canadian differences: Alberta observes DST, but Yukon now stays on MST year-round. Saskatchewan, though in the Mountain Time Zone geographically, uses Central Standard Time year-round.

How to Convert Mountain Time

Converting Mountain Time requires knowing whether DST is in effect:

During Standard Time (MST, roughly Nov–Mar):

• MST to UTC: Add 7 hours (Example: 9:00 AM MST → 4:00 PM UTC)

• MST to EST: Add 2 hours (Example: 9:00 AM MST → 11:00 AM EST)

• MST to PST: Subtract 1 hour (Example: 9:00 AM MST → 8:00 AM PST)

During Daylight Time (MDT, roughly Mar–Nov):

• MDT to UTC: Add 6 hours (Example: 9:00 AM MDT → 3:00 PM UTC)

• MDT to EDT: Add 2 hours (Example: 9:00 AM MDT → 11:00 AM EDT)

• MDT to PDT: Subtract 1 hour (Example: 9:00 AM MDT → 8:00 AM PDT)

For Arizona (except Navajo Nation), always use MST conversions regardless of date.

Time Difference with MST

Time differences between Mountain Standard Time (MST, UTC−7) and major world time zones:

Conclusion

Mountain Standard Time covers some of the most dramatic landscapes in North America — from the snow-capped Rockies to the searing Arizona desert. It's the least populated of the four continental US time zones, but it's home to fast-growing metros like Phoenix and Denver, world-famous ski resorts, and some of the country's most visited national parks.

The Arizona exception makes MST one of the trickier time zones to navigate. Scheduling a call between Phoenix and Denver requires checking the calendar. Planning a road trip through Navajo and Hopi lands means your phone might change time zones half a dozen times. But once you understand the quirks, Mountain Time isn't so complicated — just don't forget to ask whether someone's in Arizona before setting up that meeting.