BST to IRST Time Converter
IRST is 2 hours and 30 minutes ahead of BST. BST is UTC+1:00, and IRST is UTC+3:30.
Best Time to Call Between BST and IRST
Both zones are inside normal business hours between 9:00 AM and 3:00 PM BST — that's 11:30 AM to 5:30 PM IRST. That's a 6-hour window.
both at work BST only IRST only neither — hours along the strip are BST.
Common Times Converted
BST on the left, IRST on the right.
BST to IRST: Full 24-Hour Conversion Table
Shaded rows are working hours; the darker shade marks the hours when both zones are at work.
| BST | 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 | BST only |
| 4:00 PM | 6:30 PM | BST 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 BST and IRST Actually Are
BST — British Summer Time
London, Manchester, Birmingham, Glasgow, and the rest of the UK from late March to late October. Standing at UTC+1:00 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, October 25, 2026, to GMT. BST also stands for Bangladesh Standard Time (UTC+6). BDT is the clearer label for that one.
British Summer Time began in 1916 as a wartime fuel-saving measure and has run every year since, making it one of the oldest continuous daylight saving schemes in the world.
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
BST 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 BST
Cities on IRST
Frequently Asked Questions
What is the time difference between BST and IRST?
IRST is 2 hours and 30 minutes ahead of BST.
What is 9:00 AM BST in IRST?
9:00 AM BST is 11:30 AM IRST.
What are the best hours to schedule a call between BST and IRST?
Between 9:00 AM and 3:00 PM BST, which is 11:30 AM to 5:30 PM IRST. Both sides are inside normal business hours through that window.
Does the difference between BST and IRST change during the year?
Yes. BST 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 BST always mean British Summer Time?
BST also stands for Bangladesh Standard Time (UTC+6). BDT is the clearer label for that one.
Does IRST always mean Iran Standard Time?
Iran abolished daylight saving in 2022, so the half-hour offset now holds all year.