IRST to MST Time Converter
MST is 9 hours and 30 minutes behind IRST. IRST is UTC+3:30, and The US Mountain states are currently on MDT (UTC-6:00).
Best Time to Call Between IRST and MST
Standard 9-to-5 hours in these two zones never overlap, so someone has to take the call outside their working day. The most workable window is 5:00 PM to 10:00 PM IRST, which is 7:30 AM to 12:30 PM MST.
both at work IRST only MST only neither — hours along the strip are IRST.
Common Times Converted
IRST on the left, MST on the right.
IRST to MST: Full 24-Hour Conversion Table
Shaded rows are working hours; the darker shade marks the hours when both zones are at work.
| IRST | MST | Working hours |
|---|---|---|
| 12:00 AM | 2:30 PM prev day | MST only |
| 1:00 AM | 3:30 PM prev day | MST only |
| 2:00 AM | 4:30 PM prev day | MST only |
| 3:00 AM | 5:30 PM prev day | — |
| 4:00 AM | 6:30 PM prev day | — |
| 5:00 AM | 7:30 PM prev day | — |
| 6:00 AM | 8:30 PM prev day | — |
| 7:00 AM | 9:30 PM prev day | — |
| 8:00 AM | 10:30 PM prev day | — |
| 9:00 AM | 11:30 PM prev day | IRST only |
| 10:00 AM | 12:30 AM | IRST only |
| 11:00 AM | 1:30 AM | IRST only |
| 12:00 PM | 2:30 AM | IRST only |
| 1:00 PM | 3:30 AM | IRST only |
| 2:00 PM | 4:30 AM | IRST only |
| 3:00 PM | 5:30 AM | IRST only |
| 4:00 PM | 6:30 AM | IRST only |
| 5:00 PM | 7:30 AM | — |
| 6:00 PM | 8:30 AM | — |
| 7:00 PM | 9:30 AM | MST only |
| 8:00 PM | 10:30 AM | MST only |
| 9:00 PM | 11:30 AM | MST only |
| 10:00 PM | 12:30 PM | MST only |
| 11:00 PM | 1:30 PM | MST only |
What IRST and MST Actually Are
IRST — Iran Standard Time
Tehran, Mashhad, Isfahan. Standing at UTC+3:30 as written, and the region does not change its clocks, so that offset holds all year. Iran abolished daylight saving in 2022, so the half-hour offset now holds all year.
Iran abolished daylight saving in 2022. Its half-hour offset is a deliberate compromise between the solar times of its western and eastern borders.
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
Expect times on the half hour
IRST sits on a 30-minute offset rather than a whole hour, so a round number on one side is never a round number on the other. A 9:00 meeting becomes 30 minutes past the hour, which is exactly the detail calendar invitations get wrong when someone converts in their head.
The date changes mid-working-day
For 1 of the eight hours in a normal IRST working day, the equivalent MST time falls on a different calendar date. Anything scheduled in that stretch needs the date checked as well as the time, or a Tuesday call quietly becomes a Wednesday one at the other end.
This gap is not fixed
MST changes its clocks and IRST 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 IRST
Cities on MST
Frequently Asked Questions
What is the time difference between IRST and MST?
MST is 9 hours and 30 minutes behind IRST. That is the live figure. Taken strictly as written, the gap between IRST and MST is 10 hours and 30 minutes — the two differ because at least one of these regions is currently on daylight saving.
What is 9:00 AM IRST in MST?
9:00 AM IRST is 11:30 PM the previous day MST.
What are the best hours to schedule a call between IRST and MST?
Standard business hours in these two zones do not overlap at all, so one side has to work outside the 9-to-5. The most workable window is 5:00 PM to 10:00 PM IRST, which is 7:30 AM to 12:30 PM MST.
Does the difference between IRST and MST change during the year?
Yes. MST observes daylight saving and IRST 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 IRST always mean Iran Standard Time?
Iran abolished daylight saving in 2022, so the half-hour offset now holds all year.
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.