Convert BST to IRST
IRST is 2 hours 30 minutes ahead of BST. BST is UTC+1 and IRST is UTC+3:30.
Right now: BST · IRST
Which BST is this?
BST names more than one zone. This page reads it as British Summer Time at UTC+1, which is the reading most converters take. There is one other: Bangladesh Standard Time at UTC+6, used in Bangladesh, all year.
The letters on a meeting invitation do not say which one is meant. If yours is not British Summer Time, the answer above is wrong, and not by a little:
| If BST means | Then |
|---|---|
| British Summer Time — assumed on this page | IRST is 2.5 hours ahead of BST |
| Bangladesh Standard Time | IRST is 2.5 hours behind BST |
The large converter sites disagree about this as well: search for a BST conversion and some of the results answer for one reading and some for another, none of them saying which they chose. Where it matters, ask which country the sender is in rather than which letters they typed.
Best time to schedule a meeting
Standard 9–5 working hours overlap for 6 hours: 9:00 AM–3:00 PM BST (11:00 AM–5:00 PM IRST). Schedule meetings inside that window.
| BST | IRST | Suitable? |
|---|---|---|
| 9:00 AM | 11:30 AM | working hours |
| 10:00 AM | 12:30 PM | working hours |
| 11:00 AM | 1:30 PM | working hours |
| 12:00 PM | 2:30 PM | working hours |
| 1:00 PM | 3:30 PM | working hours |
| 2:00 PM | 4:30 PM | working hours |
| 3:00 PM | 5:30 PM | outside 9–5 |
| 4:00 PM | 6:30 PM | outside 9–5 |
| 5:00 PM | 7:30 PM | outside 9–5 |
BST to IRST conversion table
| BST | IRST |
|---|---|
| 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 |
| 8:00 AM | 10:30 AM |
| 9:00 AM | 11:30 AM |
| 10:00 AM | 12:30 PM |
| 11:00 AM | 1:30 PM |
| 12:00 PM | 2:30 PM |
| 1:00 PM | 3:30 PM |
| 2:00 PM | 4:30 PM |
| 3:00 PM | 5:30 PM |
| 4:00 PM | 6:30 PM |
| 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) |
About BST
British Summer Time (BST) is UTC+1. It is used in the UK from late March to late October.
British Summer Time is UTC+1, in force in the UK and Ireland from the last Sunday in March to the last Sunday in October. The abbreviation is ambiguous: BST also means Bangladesh Standard Time, UTC+6, five hours away. Within the UK it is the reason "GMT" is wrong for most of the year — the clocks are on BST from spring to autumn, and only the winter half of the year is actually GMT.
About IRST
Iran Standard Time (IRST) is UTC+3:30. It is used in Iran, all year.
Iran Standard Time is UTC+3:30. Iran ran daylight saving for decades and stopped in 2022, so material written before then puts the country half an hour further ahead in summer and is now wrong. Half-hour offsets are rare enough that scheduling tools sometimes round them, which turns a correct calculation into a thirty-minute error.
Does this gap change with the seasons?
This gap is seasonal. The abbreviations themselves are fixed offsets, but the region on BST switches to GMT (UTC+0) from late October to late March. So the 2.5-hour figure on this page is correct for the part of the year when both places are actually on these abbreviations, and changes by an hour outside it.
IRST does not shift, so the whole change comes from one side. A recurring meeting fixed in IRST will appear to move by an hour for everyone on the other side, twice a year, without anyone changing anything.
This is the reason scheduling systems store an IANA zone such as Region/City rather than an offset or an abbreviation: the zone knows its own rules and the offset does not.
Frequently asked questions
What time is 9:00 AM BST in IRST?
9:00 AM BST is 11:30 AM IRST.
Is IRST ahead of BST?
IRST is 2 hours 30 minutes ahead of BST.
Which time zone does this use?
BST is UTC+1 and IRST is UTC+3:30. Both abbreviations denote a single fixed offset, so this conversion never shifts with daylight saving — what changes is which abbreviation a place is using at the time.