AST to MST Time Converter
MST is 3 hours behind AST. Atlantic Canada and the Caribbean are currently on ADT (UTC-3:00), and The US Mountain states are currently on MDT (UTC-6:00).
Best Time to Call Between AST and MST
Both zones are inside normal business hours between 12:00 PM and 5:00 PM AST — that's 9:00 AM to 2:00 PM MST. That's a 5-hour window.
both at work AST only MST only neither — hours along the strip are AST.
Common Times Converted
AST on the left, MST on the right.
AST to MST: Full 24-Hour Conversion Table
Shaded rows are working hours; the darker shade marks the hours when both zones are at work.
| AST | MST | Working hours |
|---|---|---|
| 12:00 AM | 9:00 PM prev day | — |
| 1:00 AM | 10:00 PM prev day | — |
| 2:00 AM | 11:00 PM prev day | — |
| 3:00 AM | 12:00 AM | — |
| 4:00 AM | 1:00 AM | — |
| 5:00 AM | 2:00 AM | — |
| 6:00 AM | 3:00 AM | — |
| 7:00 AM | 4:00 AM | — |
| 8:00 AM | 5:00 AM | — |
| 9:00 AM | 6:00 AM | AST only |
| 10:00 AM | 7:00 AM | AST only |
| 11:00 AM | 8:00 AM | AST only |
| 12:00 PM | 9:00 AM | Both zones |
| 1:00 PM | 10:00 AM | Both zones |
| 2:00 PM | 11:00 AM | Both zones |
| 3:00 PM | 12:00 PM | Both zones |
| 4:00 PM | 1:00 PM | Both zones |
| 5:00 PM | 2:00 PM | MST only |
| 6:00 PM | 3:00 PM | MST only |
| 7:00 PM | 4:00 PM | MST only |
| 8:00 PM | 5:00 PM | — |
| 9:00 PM | 6:00 PM | — |
| 10:00 PM | 7:00 PM | — |
| 11:00 PM | 8:00 PM | — |
What AST and MST Actually Are
AST — Atlantic Standard Time
Halifax, San Juan, Santo Domingo, Bermuda. Standing at UTC-4:00 as written, and the region does change its clocks, so its live offset moves by an hour twice a year. The next change is on Sunday, November 1, 2026, to AST. AST also stands for Arabia Standard Time (UTC+3), used in Saudi Arabia, Iraq and Kuwait.
Atlantic Standard Time is the only North American zone whose name is more commonly associated, worldwide, with a completely different zone — Arabia Standard Time.
MST — Mountain Standard Time
Denver, Salt Lake City, Calgary — and Phoenix year-round. Standing at UTC-7:00 as written, and the region does change its clocks, so its live offset moves by an hour twice a year. The next change is on Sunday, November 1, 2026, to MST. Arizona stays on MST all year, so Phoenix and Denver are an hour apart for eight months and identical for four.
Arizona has stayed on MST year-round since 1968 — the Navajo Nation within it does observe daylight saving, making the state a patchwork.
What This Means in Practice
Both sides change clocks, on different dates
Both regions observe daylight saving but do not switch on the same day, so for a week or two each spring and fall the gap between them is an hour different from the rest of the year. Those short windows are where recurring invitations quietly break.
Major Cities in Each Zone
Cities on AST
Cities on MST
Frequently Asked Questions
What is the time difference between AST and MST?
MST is 3 hours behind AST.
What is 9:00 AM AST in MST?
9:00 AM AST is 6:00 AM MST.
What are the best hours to schedule a call between AST and MST?
Between 12:00 PM and 5:00 PM AST, which is 9:00 AM to 2:00 PM MST. Both sides are inside normal business hours through that window.
Does the difference between AST and MST change during the year?
Yes. Both regions observe daylight saving, and they do not switch on the same dates, so the gap shifts by an hour at least twice a year. The next clock change is on Sunday, November 1, 2026.
Does AST always mean Atlantic Standard Time?
AST also stands for Arabia Standard Time (UTC+3), used in Saudi Arabia, Iraq and Kuwait.
Does MST always mean Mountain Standard Time?
Arizona stays on MST all year, so Phoenix and Denver are an hour apart for eight months and identical for four.