MST to AST Time Converter
AST is 3 hours ahead of MST. The US Mountain states are currently on MDT (UTC-6:00), and Atlantic Canada and the Caribbean are currently on ADT (UTC-3:00).
Best Time to Call Between MST and AST
Both zones are inside normal business hours between 9:00 AM and 2:00 PM MST — that's 12:00 PM to 5:00 PM AST. That's a 5-hour window.
both at work MST only AST only neither — hours along the strip are MST.
Common Times Converted
MST on the left, AST on the right.
MST to AST: Full 24-Hour Conversion Table
Shaded rows are working hours; the darker shade marks the hours when both zones are at work.
| MST | AST | Working hours |
|---|---|---|
| 12:00 AM | 3:00 AM | — |
| 1:00 AM | 4:00 AM | — |
| 2:00 AM | 5:00 AM | — |
| 3:00 AM | 6:00 AM | — |
| 4:00 AM | 7:00 AM | — |
| 5:00 AM | 8:00 AM | — |
| 6:00 AM | 9:00 AM | AST only |
| 7:00 AM | 10:00 AM | AST only |
| 8:00 AM | 11:00 AM | AST only |
| 9:00 AM | 12:00 PM | Both zones |
| 10:00 AM | 1:00 PM | Both zones |
| 11:00 AM | 2:00 PM | Both zones |
| 12:00 PM | 3:00 PM | Both zones |
| 1:00 PM | 4:00 PM | Both zones |
| 2:00 PM | 5:00 PM | MST only |
| 3:00 PM | 6:00 PM | MST only |
| 4:00 PM | 7:00 PM | MST only |
| 5:00 PM | 8:00 PM | — |
| 6:00 PM | 9:00 PM | — |
| 7:00 PM | 10:00 PM | — |
| 8:00 PM | 11:00 PM | — |
| 9:00 PM | 12:00 AM next day | — |
| 10:00 PM | 1:00 AM next day | — |
| 11:00 PM | 2:00 AM next day | — |
What MST and AST Actually Are
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.
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.
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 MST
Cities on AST
Frequently Asked Questions
What is the time difference between MST and AST?
AST is 3 hours ahead of MST.
What is 9:00 AM MST in AST?
9:00 AM MST is 12:00 PM AST.
What are the best hours to schedule a call between MST and AST?
Between 9:00 AM and 2:00 PM MST, which is 12:00 PM to 5:00 PM AST. Both sides are inside normal business hours through that window.
Does the difference between MST and AST 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 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.
Does AST always mean Atlantic Standard Time?
AST also stands for Arabia Standard Time (UTC+3), used in Saudi Arabia, Iraq and Kuwait.