The mountain time abbreviation you can use any day of the year is MT, for Mountain Time. Two more exact forms name the season: MST, Mountain Standard Time, for the cold months, and MDT, Mountain Daylight Time, from spring to fall.
The zone covers the Rocky Mountain states and a strip of the Great Plains. It sits seven hours behind Coordinated Universal Time in winter and six hours behind in summer. One state makes things tricky: most of Arizona stays on MST all year and never switches to MDT.
Quick facts
General form
MT, Mountain TimeWinter form
MST, Mountain Standard Time (UTC minus 7)Summer form
MDT, Mountain Daylight Time (UTC minus 6)Periods
None: MT, MST, MDTBig exception
Most of Arizona uses MST all yearNeighbors
One hour ahead of Pacific, one hour behind Central
Which mountain time abbreviation fits the date?
| Label | Full name | When it applies | Offset |
|---|---|---|---|
| MT | Mountain Time | Any time of year | Depends on season |
| MST | Mountain Standard Time | First Sunday in November to second Sunday in March | UTC minus 7 |
| MDT | Mountain Daylight Time | Second Sunday in March to first Sunday in November | UTC minus 6 |
The clocks change at 2 a.m. local time on those Sundays. If you are writing a date in July, MDT is the precise label. In January, MST is right. If you are not sure, or the message covers both seasons, the plain abbreviation for mountain time, MT, never goes wrong.
States and places on Mountain Time
Six states keep all or nearly all of their land on Mountain Time: Colorado, Utah, New Mexico, Wyoming, Montana and Arizona. Several more are split between two zones:
- Idaho: the southern part, including Boise, is Mountain. The northern panhandle is Pacific.
- Oregon: most of Malheur County, on the Idaho border, uses Mountain Time.
- Texas: El Paso and its corner of West Texas.
- Kansas, Nebraska and the Dakotas: their western edges.
- Nevada: the border town of West Wendover.
In Canada, Alberta and parts of British Columbia and the Northwest Territories also follow the zone. If you are writing a state name rather than a zone, the Colorado abbreviation page covers CO and Colo.
The Arizona exception
Most of Arizona does not move its clocks in March. It stays on Mountain Standard Time year round, so in summer Phoenix shows the same time as Los Angeles, and in winter it matches Denver. The Navajo Nation, in the northeast of the state, does observe daylight saving time, while the Hopi lands inside it do not.
A webinar invite: "Starts at 10 a.m. MST (Phoenix)." Writing MST in July is correct here, because Arizona never uses MDT. For a Denver audience in July, the same line should say MDT or simply MT.
How to write the abbreviation for mountain time
- Use capital letters with no periods: MT, MST, MDT.
- Put the zone after the time: 3:30 p.m. MT. The a.m. and p.m. page covers the hour part.
- In running text, spell it out the first time: "Mountain Time (MT)."
- Capitalize Mountain when it names the zone, even in lowercase style guides that keep the word "time" lowercase.
- Avoid writing MST for a summer date in Colorado or Utah. It is one hour off.
For more everyday short forms like these, see the common abbreviations guide.
Converting Mountain Time to other US zones
Mountain Time is one step west of Central and one step east of Pacific. A quick way to convert:
| Zone | Same moment |
|---|---|
| Pacific | 11 a.m. |
| Mountain | 12 p.m. (noon) |
| Central | 1 p.m. |
| Eastern | 2 p.m. |
Summer Arizona breaks the pattern and lines up with Pacific. For neighboring zones, read the Central Time and Eastern Time pages, and GMT for the world reference clock.
Labels that get mixed up
- MT vs MST: MT is seasonless. MST is winter only, except in Arizona.
- MDT vs MST: the D means daylight, the S means standard.
- MT as a state: MT is also the postal code for Montana. A line like "Helena, MT" is a place, not a time.
- Mountain vs Pacific: Nevada is mostly Pacific, even though it sits beside Utah and Arizona.
Questions people ask
What is the abbreviation for mountain time?
MT is the general one. Add S or D for the season: MST in winter, MDT in summer.
Is it MST or MDT right now?
From the second Sunday in March to the first Sunday in November, most of the zone is on MDT. From November to March it is MST. Most of Arizona is on MST every day of the year.
What is the difference between Mountain Time and Pacific Time?
Mountain Time is one hour ahead. When it is 9 a.m. in Denver, it is 8 a.m. in Seattle, except in summer Arizona, which matches Pacific.
Is Denver on Mountain Time?
Yes. All of Colorado is on Mountain Time and switches between MST and MDT.
Do you put periods in MST?
No. Zone labels use plain capitals and skip periods: MT, MST, MDT.