MST to AST: MST is 3 hours behind AST

Mountain Time is 3 hours behind Atlantic Time, on every day of the year. It is 7:04 pm MDT in Mountain and 10:04 pm ADT in Atlantic.

Convert a specific time from MST to AST

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 MST and AST?

Atlantic Time is 3 hours ahead of Mountain Time. To go from MST to AST you add 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.

MST to AST conversion table

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

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

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

Does daylight saving change MST to AST?

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.

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.

Is MST ahead of or behind AST?

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

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

Questions

What is MST in AST?

MST is 3 hours behind AST. 9:00 am MST is 12:00 pm AST.

How many hours ahead is AST of MST?

AST is 3 hours ahead of MST.

What time is it in Atlantic right now?

10:04 pm ADT on Thursday, September 24, 2026.

When can Mountain and Atlantic meet during working hours?

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

Does this account for daylight saving?

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

Other conversions

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