Mountain Daylight Time is UTC−06:00, the summer offset for most of the North American Mountain Time zone.
Detecting your timezone for a personal comparison…
Now
MDT is not used in most of Arizona. During summer, Denver on MDT matches Phoenix on MST, while in winter Denver falls an hour behind Phoenix. That seasonal alignment is one of the more confusing US time relationships.
The offset shown above is computed from America/Denver at page render time using Intl.DateTimeFormat. It can change when daylight saving starts or ends.
When daylight saving ends, Mountain Time in Denver returns to MST (UTC−07:00).
Mountain Daylight Time (MDT) uses the IANA identifier America/Denver. Mountain Daylight Time is UTC−06:00, the summer offset for most of the North American Mountain Time zone.
Right now Mountain Daylight Time is UTC-06:00. The live abbreviation reported by the timezone database is MDT.
Daylight saving time is in effect. Standard time is labeled MST and daylight time is labeled MDT. Dates are taken from IANA data, not hardcoded on this site.
Use the converter with America/Denver as the source zone, or open the Time Zone Converter and pick a city that uses MDT. Offsets update automatically when daylight saving begins or ends.