The Mountain Time Zone of North America keeps time by subtracting seven hours from Greenwich Mean Time , during the shortest days of autumn and winter ( UTC − 7 ) , and by subtracting six hours during daylight saving time in the spring , summer , and early autumn ( UTC − 6 ) .
The Mountain Time Zone subtracts seven hours from UTC during standard time ( UTC-7 ) and six hours during daylight saving time ( UTC-6 ) .