Technical Specifications & Standards
Official chronometric properties, ISO standards, and international database registry identifiers for Mountain Daylight Time:
Daylight Saving Time (DST) Transitions
⬆️ Spring Forward (Clocks Advance)
Second Sunday in March at 02:00 AM (Clocks advance to MDT)
⬇️ Fall Back (Clocks Return)
First Sunday in November at 02:00 AM (Clocks return to MST)
Observing Jurisdictions & Subdivisions
2 Sovereign NationsSovereign nations, administrative subdivisions, and regional territories officially operating under MDT:
Regional Subdivisions & Territory Details
Financial Markets & Trading Hours
Puts Rocky Mountain businesses on UTC-6, sharing the same clock time as standard-time Midwest hubs during the summer.
Local Hours: 08:30 - 16:30 MDT
UTC Window: 15:00 - 23:00 UTC
Local Hours: 08:30 - 16:30 MDT
UTC Window: 15:00 - 23:00 UTC
Major Cities in MDT
Primary metropolitan centers and financial hubs observing this time zone:
Adoption History & Astronomical Facts
Year Established: 1918
First enacted in 1918 to keep coal, copper, and silver mining operations running under daylight conditions across the Rockies during the industrial push of the war.
Because Arizona stays on UTC-7 while Colorado moves to MDT (UTC-6), driving east from Flagstaff to Albuquerque in July requires moving your watch forward one full hour.
Frequently Asked Questions about MDT
What does MDT stand for?
MDT stands for Mountain Daylight Time, running at UTC-6 across the Rocky Mountain region between March and November.
Is MDT the same as MST?
No. MDT is used during summer at UTC-6, while MST is the winter schedule at UTC-7.
How many hours behind New York is MDT?
MDT is two hours behind Eastern Daylight Time (EDT). When it is 3:00 PM in New York, it is 1:00 PM in Denver.