Mountain Standard Time (MST) is the opposite of Mountain Daylight Time (MDT). Mountain Standard Time and Mountain Daylight Time are both 7 hours behind Coordinated Universal Time (UTC).
Occasionally, MDT and MST are both stated as UTC -6 hours and -0600, respectively. Mountain Standard Time is used in many western US states in the winter, and Mountain Daylight Time in the summer.
This pattern is followed in some states in some regions but not in others. In certain of the western mountainous regions of Canada and Mexico, MDT and MST are also in use.