GMT to IRST Time Converter
IRST is 2 hours and 30 minutes ahead of GMT. The UK and Ireland are currently on BST (UTC+1:00), and IRST is UTC+3:30.
Best Time to Call Between GMT and IRST
Both zones are inside normal business hours between 9:00 AM and 3:00 PM GMT — that's 11:30 AM to 5:30 PM IRST. That's a 6-hour window.
both at work GMT only IRST only neither — hours along the strip are GMT.
Common Times Converted
GMT on the left, IRST on the right.
GMT to IRST: Full 24-Hour Conversion Table
Shaded rows are working hours; the darker shade marks the hours when both zones are at work.
| GMT | IRST | Working hours |
|---|---|---|
| 12:00 AM | 2:30 AM | — |
| 1:00 AM | 3:30 AM | — |
| 2:00 AM | 4:30 AM | — |
| 3:00 AM | 5:30 AM | — |
| 4:00 AM | 6:30 AM | — |
| 5:00 AM | 7:30 AM | — |
| 6:00 AM | 8:30 AM | — |
| 7:00 AM | 9:30 AM | IRST only |
| 8:00 AM | 10:30 AM | IRST only |
| 9:00 AM | 11:30 AM | Both zones |
| 10:00 AM | 12:30 PM | Both zones |
| 11:00 AM | 1:30 PM | Both zones |
| 12:00 PM | 2:30 PM | Both zones |
| 1:00 PM | 3:30 PM | Both zones |
| 2:00 PM | 4:30 PM | Both zones |
| 3:00 PM | 5:30 PM | GMT only |
| 4:00 PM | 6:30 PM | GMT only |
| 5:00 PM | 7:30 PM | — |
| 6:00 PM | 8:30 PM | — |
| 7:00 PM | 9:30 PM | — |
| 8:00 PM | 10:30 PM | — |
| 9:00 PM | 11:30 PM | — |
| 10:00 PM | 12:30 AM next day | — |
| 11:00 PM | 1:30 AM next day | — |
What GMT and IRST Actually Are
GMT — Greenwich Mean Time
The UK and Ireland in winter, plus Iceland, Portugal and much of West Africa. Standing at UTC 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, October 25, 2026, to GMT. Often used loosely as a synonym for UTC. They differ by less than a second, so for scheduling they are interchangeable.
Britain ran an experiment from 1968 to 1971 on permanent UTC+1, abandoning GMT entirely. It was scrapped after complaints about dark winter mornings in Scotland.
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.
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.
This gap is not fixed
GMT 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, October 25, 2026 unless someone resets it.
Major Cities in Each Zone
Cities on GMT
Cities on IRST
Frequently Asked Questions
What is the time difference between GMT and IRST?
IRST is 2 hours and 30 minutes ahead of GMT. That is the live figure. Taken strictly as written, the gap between GMT and IRST is 3 hours and 30 minutes — the two differ because at least one of these regions is currently on daylight saving.
What is 9:00 AM GMT in IRST?
9:00 AM GMT is 11:30 AM IRST.
What are the best hours to schedule a call between GMT and IRST?
Between 9:00 AM and 3:00 PM GMT, which is 11:30 AM to 5:30 PM IRST. Both sides are inside normal business hours through that window.
Does the difference between GMT and IRST change during the year?
Yes. GMT 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, October 25, 2026.
Does GMT always mean Greenwich Mean Time?
Often used loosely as a synonym for UTC. They differ by less than a second, so for scheduling they are interchangeable.
Does IRST always mean Iran Standard Time?
Iran abolished daylight saving in 2022, so the half-hour offset now holds all year.