IRST to BST Time Converter
BST is 2 hours and 30 minutes behind IRST. IRST is UTC+3:30, and BST is UTC+1:00.
Best Time to Call Between IRST and BST
Both zones are inside normal business hours between 12:00 PM and 5:00 PM IRST — that's 9:30 AM to 2:30 PM BST. That's a 5-hour window.
both at work IRST only BST only neither — hours along the strip are IRST.
Common Times Converted
IRST on the left, BST on the right.
IRST to BST: Full 24-Hour Conversion Table
Shaded rows are working hours; the darker shade marks the hours when both zones are at work.
| IRST | BST | Working hours |
|---|---|---|
| 12:00 AM | 9:30 PM prev day | — |
| 1:00 AM | 10:30 PM prev day | — |
| 2:00 AM | 11:30 PM prev day | — |
| 3:00 AM | 12:30 AM | — |
| 4:00 AM | 1:30 AM | — |
| 5:00 AM | 2:30 AM | — |
| 6:00 AM | 3:30 AM | — |
| 7:00 AM | 4:30 AM | — |
| 8:00 AM | 5:30 AM | — |
| 9:00 AM | 6:30 AM | IRST only |
| 10:00 AM | 7:30 AM | IRST only |
| 11:00 AM | 8:30 AM | IRST only |
| 12:00 PM | 9:30 AM | Both zones |
| 1:00 PM | 10:30 AM | Both zones |
| 2:00 PM | 11:30 AM | Both zones |
| 3:00 PM | 12:30 PM | Both zones |
| 4:00 PM | 1:30 PM | Both zones |
| 5:00 PM | 2:30 PM | BST only |
| 6:00 PM | 3:30 PM | BST only |
| 7:00 PM | 4:30 PM | BST only |
| 8:00 PM | 5:30 PM | — |
| 9:00 PM | 6:30 PM | — |
| 10:00 PM | 7:30 PM | — |
| 11:00 PM | 8:30 PM | — |
What IRST and BST 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.
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.
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 IRST
Cities on BST
Frequently Asked Questions
What is the time difference between IRST and BST?
BST is 2 hours and 30 minutes behind IRST.
What is 9:00 AM IRST in BST?
9:00 AM IRST is 6:30 AM BST.
What are the best hours to schedule a call between IRST and BST?
Between 12:00 PM and 5:00 PM IRST, which is 9:30 AM to 2:30 PM BST. Both sides are inside normal business hours through that window.
Does the difference between IRST and BST 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 IRST always mean Iran Standard Time?
Iran abolished daylight saving in 2022, so the half-hour offset now holds all year.
Does BST always mean British Summer Time?
BST also stands for Bangladesh Standard Time (UTC+6). BDT is the clearer label for that one.