MST to AST Converter
AST is 3 hours ahead of MST. 9:00 AM MST = 12:00 PM AST.
AST is 3 hours ahead of MST. To convert MST to AST, add 3 hours to the MST time: 9:00 AM MST = 12:00 PM AST.
MST (Mountain Time) is used in Denver, Salt Lake City, Albuquerque, Calgary, Edmonton; Phoenix (Arizona) all year. AST (Atlantic Time) is used in Nova Scotia, New Brunswick, PEI; Puerto Rico and the Eastern Caribbean (all year).
Most of Arizona uses MST all year and does not switch to MDT. AST here is Atlantic Standard Time, not Arabia Standard Time.
MST to AST time conversion table
MST to AST on 6 Nov 2026. Today's date. Highlighted rows are 9 AM–5 PM in both places.
| MST | AST | Day |
|---|---|---|
| 12:00 AM MST | 3:00 AM AST | night |
| 1:00 AM MST | 4:00 AM AST | night |
| 2:00 AM MST | 5:00 AM AST | night |
| 3:00 AM MST | 6:00 AM AST | — |
| 4:00 AM MST | 7:00 AM AST | — |
| 5:00 AM MST | 8:00 AM AST | — |
| 6:00 AM MST | 9:00 AM AST | — |
| 7:00 AM MST | 10:00 AM AST | — |
| 8:00 AM MST | 11:00 AM AST | — |
| 9:00 AM MST | 12:00 PM AST | work hours |
| 10:00 AM MST | 1:00 PM AST | work hours |
| 11:00 AM MST | 2:00 PM AST | work hours |
| 12:00 PM MST | 3:00 PM AST | work hours |
| 1:00 PM MST | 4:00 PM AST | work hours |
| 2:00 PM MST | 5:00 PM AST | — |
| 3:00 PM MST | 6:00 PM AST | — |
| 4:00 PM MST | 7:00 PM AST | — |
| 5:00 PM MST | 8:00 PM AST | — |
| 6:00 PM MST | 9:00 PM AST | — |
| 7:00 PM MST | 10:00 PM AST | night |
| 8:00 PM MST | 11:00 PM AST | night |
| 9:00 PM MST | 12:00 AM AST | next day |
| 10:00 PM MST | 1:00 AM AST | next day |
| 11:00 PM MST | 2:00 AM AST | next day |
- Work rows — 9 AM–5 PM in both places
- Night in the destination (10 PM–6 AM)
How to convert MST to AST
Add 3 hours to the MST time to get AST.
Example: 9:00 AM MST = 12:00 PM AST.
Across midnight: 10:00 PM MST = 1:00 AM AST (next day). The date changes, so always check the day as well as the hour.
Time difference between MST and AST
The time difference between MST and AST is 3 hours all year – AST is ahead of MST.
MST and AST during daylight saving time
- MST next changes on 14 Mar 2027: clocks go forward one hour at 01:59 local time, from MST (UTC−7) to MDT (UTC−6).
- AST next changes on 14 Mar 2027: clocks go forward one hour at 01:59 local time, from AST (UTC−4) to ADT (UTC−3).
Best time for a meeting between MST and AST
MST and AST share 5 hours of the 9 AM–5 PM working day. Any time between 9:00 AM and 2:00 PM MST lands between 12:00 PM and 5:00 PM AST, inside working hours for both.
MST to AST FAQ
What is the time difference between MST and AST?
AST is 3 hours ahead of MST all year. 9:00 AM MST = 12:00 PM AST.
What is 9 AM MST in AST?
9:00 AM MST is 12:00 PM AST.
What is 12 PM (noon) MST in AST?
12:00 PM MST is 3:00 PM AST.
Is AST ahead of or behind MST?
AST is 3 hours ahead of MST, so it is later in AST than in MST.
Does MST change for daylight saving time?
Yes. MST next changes on 14 Mar 2027, when clocks go forward one hour from MST to MDT.
Does AST change for daylight saving time?
Yes. AST next changes on 14 Mar 2027, when clocks go forward one hour from AST to ADT.
What is the best time for a meeting between MST and AST?
MST and AST share 5 hours of the 9 AM–5 PM working day. Any time between 9:00 AM and 2:00 PM MST lands between 12:00 PM and 5:00 PM AST, inside working hours for both.
Is MT the same as MST?
MST is the winter (standard) name of Mountain Time (MT). From March to November the same clocks are called MDT. This converter always uses the one in force on the date you choose.
Related conversions
Convert AST to MST
Convert MST to other time zones
Convert other time zones to AST
Learn more
Updated 6 November 2026. Time zone data: IANA tz database.