What is AST in MST?
Mountain Time is 3 hours behind
Atlantic Time is on UTC−3:00 and Mountain Time is on UTC−6:00 right now. Both are on daylight saving, so their clocks read ADT and MDT. That gap holds all year, because both zones change their clocks together.
- Time in Halifax
- 11:13 pm
- Time in Denver
- 8:13 pm
- Difference
- −3 h
- Next clock change
- November 1, 2026
Convert a time
MDT — Mountain Time
8:00 pm
Tue
Daylight saving
Atlantic Time
Clocks go back one hour at 2am local time, becoming AST.
Mountain Time
Clocks go back one hour at 2am local time, becoming MST.
AST to MST conversion table
Every hour of Tuesday, September 22, 2026, converted from Atlantic Time to Mountain Time. 3 of the 24 hours fall on a different calendar day in Denver, which is marked.
- 12:00 am ADT
- 9:00 pm MDT−1 day
- 1:00 am ADT
- 10:00 pm MDT−1 day
- 2:00 am ADT
- 11:00 pm MDT−1 day
- 3:00 am ADT
- 12:00 am MDT
- 4:00 am ADT
- 1:00 am MDT
- 5:00 am ADT
- 2:00 am MDT
- 6:00 am ADT
- 3:00 am MDT
- 7:00 am ADT
- 4:00 am MDT
- 8:00 am ADT
- 5:00 am MDT
- 9:00 am ADT
- 6:00 am MDT
- 10:00 am ADT
- 7:00 am MDT
- 11:00 am ADT
- 8:00 am MDT
- 12:00 pm ADT
- 9:00 am MDT
- 1:00 pm ADT
- 10:00 am MDT
- 2:00 pm ADT
- 11:00 am MDT
- 3:00 pm ADT
- 12:00 pm MDT
- 4:00 pm ADT
- 1:00 pm MDT
- 5:00 pm ADT
- 2:00 pm MDT
- 6:00 pm ADT
- 3:00 pm MDT
- 7:00 pm ADT
- 4:00 pm MDT
- 8:00 pm ADT
- 5:00 pm MDT
- 9:00 pm ADT
- 6:00 pm MDT
- 10:00 pm ADT
- 7:00 pm MDT
- 11:00 pm ADT
- 8:00 pm MDT
Scheduling between the two
Working hours overlap from 12:00 pm to 6:00 pm ADT, which is 9:00 am to 3:00 pm MDT. Anything inside that window falls in the normal working day at both ends.
A note on AST: it can also mean Arabia Standard Time (UTC+3). This page means Atlantic Time.
Atlantic Time (ADT) is used in Nova Scotia, New Brunswick and Puerto Rico
Mountain Time (MDT) is used in Salt Lake City, Albuquerque and Calgary. Arizona keeps MST all year and does not follow MDT.