MST to ART Time Converter
ART is 3 hours ahead of MST. The US Mountain states are currently on MDT (UTC-6:00), and ART is UTC-3:00.
Best Time to Call Between MST and ART
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 ART. That's a 5-hour window.
both at work MST only ART only neither — hours along the strip are MST.
Common Times Converted
MST on the left, ART on the right.
MST to ART: Full 24-Hour Conversion Table
Shaded rows are working hours; the darker shade marks the hours when both zones are at work.
| MST | ART | 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 | ART only |
| 7:00 AM | 10:00 AM | ART only |
| 8:00 AM | 11:00 AM | ART 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 ART 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.
ART — Argentina Time
Buenos Aires, Córdoba, Rosario. Standing at UTC-3:00 as written, and the region does not change its clocks, so that offset holds all year. Argentina does not observe daylight saving, so this offset is fixed year-round.
Argentina has changed its time zone rules more than a dozen times since 1930 and abandoned daylight saving in 2009.
What This Means in Practice
This gap is not fixed
MST changes its clocks and ART does not, so the difference between them moves by an hour twice a year. A recurring meeting set now will drift for one side from Sunday, November 1, 2026 unless someone resets it.
Major Cities in Each Zone
Cities on MST
Cities on ART
Frequently Asked Questions
What is the time difference between MST and ART?
ART is 3 hours ahead of MST. That is the live figure. Taken strictly as written, the gap between MST and ART is 4 hours — the two differ because at least one of these regions is currently on daylight saving.
What is 9:00 AM MST in ART?
9:00 AM MST is 12:00 PM ART.
What are the best hours to schedule a call between MST and ART?
Between 9:00 AM and 2:00 PM MST, which is 12:00 PM to 5:00 PM ART. Both sides are inside normal business hours through that window.
Does the difference between MST and ART change during the year?
Yes. MST observes daylight saving and ART does not, 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 ART always mean Argentina Time?
Argentina does not observe daylight saving, so this offset is fixed year-round.