What is MST in AST?
Atlantic Time is 3 hours ahead
Mountain Time is on UTC−6:00 and Atlantic Time is on UTC−3:00 right now. Both are on daylight saving, so their clocks read MDT and ADT. That gap holds all year, because both zones change their clocks together.
- Time in Denver
- 8:56 pm
- Time in Halifax
- 11:56 pm
- Difference
- +3 h
- Next clock change
- November 1, 2026
Convert a time
ADT — Atlantic Time
11:00 pm
Tue
Daylight saving
Mountain Time
Clocks go back one hour at 2am local time, becoming MST.
Atlantic Time
Clocks go back one hour at 2am local time, becoming AST.
MST to AST conversion table
Every hour of Tuesday, September 22, 2026, converted from Mountain Time to Atlantic Time. 3 of the 24 hours fall on a different calendar day in Halifax, which is marked.
- 12:00 am MDT
- 3:00 am ADT
- 1:00 am MDT
- 4:00 am ADT
- 2:00 am MDT
- 5:00 am ADT
- 3:00 am MDT
- 6:00 am ADT
- 4:00 am MDT
- 7:00 am ADT
- 5:00 am MDT
- 8:00 am ADT
- 6:00 am MDT
- 9:00 am ADT
- 7:00 am MDT
- 10:00 am ADT
- 8:00 am MDT
- 11:00 am ADT
- 9:00 am MDT
- 12:00 pm ADT
- 10:00 am MDT
- 1:00 pm ADT
- 11:00 am MDT
- 2:00 pm ADT
- 12:00 pm MDT
- 3:00 pm ADT
- 1:00 pm MDT
- 4:00 pm ADT
- 2:00 pm MDT
- 5:00 pm ADT
- 3:00 pm MDT
- 6:00 pm ADT
- 4:00 pm MDT
- 7:00 pm ADT
- 5:00 pm MDT
- 8:00 pm ADT
- 6:00 pm MDT
- 9:00 pm ADT
- 7:00 pm MDT
- 10:00 pm ADT
- 8:00 pm MDT
- 11:00 pm ADT
- 9:00 pm MDT
- 12:00 am ADT+1 day
- 10:00 pm MDT
- 1:00 am ADT+1 day
- 11:00 pm MDT
- 2:00 am ADT+1 day
Scheduling between the two
Working hours overlap from 9:00 am to 3:00 pm MDT, which is 12:00 pm to 6:00 pm ADT. 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.
Mountain Time (MDT) is used in Salt Lake City, Albuquerque and Calgary. Arizona keeps MST all year and does not follow MDT.
Atlantic Time (ADT) is used in Nova Scotia, New Brunswick and Puerto Rico