AST to MST: AST is 3 hours ahead of MST

Atlantic Time is 3 hours ahead of Mountain Time, on every day of the year. It is 8:00 pm ADT in Atlantic and 5:00 pm MDT in Mountain.

Convert a specific time from AST to MST

Pick any time and date to convert it both ways. The conversion runs in your browser against the real zone rules, so a date inside a daylight saving period gets that period's offset rather than today's.

What is the time difference between AST and MST?

Mountain Time is 3 hours behind Atlantic Time. To go from AST to MST you subtract 3 hours. That gap holds on all 365 days of 2026: both zones move their clocks, but on the same dates and in the same direction, so the distance between them never changes.

AST to MST conversion table

Every hour of Thursday, September 24, 2026 in Atlantic, with the matching reading in Mountain. 3 of the 24 hours land on a different calendar date in Mountain, which is the part people get wrong when they schedule across this pair.

What are the best hours to schedule a call between AST and MST?

5 hours of the standard 9:00 am to 5:00 pm working day line up in both zones, from 12:00 pm AST to 5:00 pm AST. In Mountain that window reads 9:00 am to 2:00 pm. Outside it, one side is either not yet at their desk or already gone.

Does daylight saving change AST to MST?

Atlantic Time is currently on ADT and changes next on Sunday, November 1, 2026, when the clock falls back from 1:59 am to 1:00 am and the offset moves from UTC-3 to UTC-4.

Mountain Time is currently on MDT and changes next on Sunday, November 1, 2026, when the clock falls back from 1:59 am to 1:00 am and the offset moves from UTC-6 to UTC-7.

Is AST ahead of or behind MST?

AST is ahead of MST by 3 hours: when it is 12:00 pm in Atlantic, it is 9:00 am in Mountain. One wrinkle worth knowing: AST and ADT are two names for the same zone, not two zones. Atlantic Time reads AST in winter and ADT in summer. When somebody types "ast to mst" they nearly always mean the zone rather than the literal winter offset, so this page resolves AST to America/Halifax and MST to America/Denver and applies whichever offset is genuinely in force on the day.

Atlantic Time covers Halifax, Moncton and the Canadian Maritimes. Mountain Time covers Denver, Salt Lake City, Albuquerque and Calgary. The identifiers behind them are America/Halifax and America/Denver, which is what any calendar or scheduling system should be storing rather than a fixed number of hours.

Questions

What is AST in MST?

AST is 3 hours ahead of MST. 9:00 am AST is 6:00 am MST.

How many hours ahead is MST of AST?

MST is 3 hours behind AST.

What time is it in Mountain right now?

5:00 pm MDT on Thursday, September 24, 2026.

When can Atlantic and Mountain meet during working hours?

Between 12:00 pm and 5:00 pm AST, which is 9:00 am to 2:00 pm MST.

Does this account for daylight saving?

Yes. Every reading is computed from the IANA database for the actual date, so ADT and MDT are the abbreviations genuinely in force today rather than a fixed assumption.

Other conversions

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