Convert GMT to IRST
IRST is 3 hours 30 minutes ahead of GMT. GMT is UTC+0 and IRST is UTC+3:30.
Right now: GMT · IRST
Best time to schedule a meeting
Standard 9–5 working hours overlap for 5 hours: 9:00 AM–2:00 PM GMT (12:00 PM–5:00 PM IRST). Schedule meetings inside that window.
| GMT | IRST | Suitable? |
|---|---|---|
| 9:00 AM | 12:30 PM | working hours |
| 10:00 AM | 1:30 PM | working hours |
| 11:00 AM | 2:30 PM | working hours |
| 12:00 PM | 3:30 PM | working hours |
| 1:00 PM | 4:30 PM | working hours |
| 2:00 PM | 5:30 PM | outside 9–5 |
| 3:00 PM | 6:30 PM | outside 9–5 |
| 4:00 PM | 7:30 PM | outside 9–5 |
| 5:00 PM | 8:30 PM | outside 9–5 |
GMT to IRST conversion table
| GMT | IRST |
|---|---|
| 12:00 AM | 3:30 AM |
| 1:00 AM | 4:30 AM |
| 2:00 AM | 5:30 AM |
| 3:00 AM | 6:30 AM |
| 4:00 AM | 7:30 AM |
| 5:00 AM | 8:30 AM |
| 6:00 AM | 9:30 AM |
| 7:00 AM | 10:30 AM |
| 8:00 AM | 11:30 AM |
| 9:00 AM | 12:30 PM |
| 10:00 AM | 1:30 PM |
| 11:00 AM | 2:30 PM |
| 12:00 PM | 3:30 PM |
| 1:00 PM | 4:30 PM |
| 2:00 PM | 5:30 PM |
| 3:00 PM | 6:30 PM |
| 4:00 PM | 7:30 PM |
| 5:00 PM | 8:30 PM |
| 6:00 PM | 9:30 PM |
| 7:00 PM | 10:30 PM |
| 8:00 PM | 11:30 PM |
| 9:00 PM | 12:30 AM (next day) |
| 10:00 PM | 1:30 AM (next day) |
| 11:00 PM | 2:30 AM (next day) |
About GMT
Greenwich Mean Time (GMT) is UTC+0. It is used in the UK and Ireland in winter, Portugal, Iceland and much of West Africa.
The trap with GMT is that the United Kingdom is not on it for most of the year. From late March to late October the UK runs BST, UTC+1, so a meeting agreed "10am GMT" with a London colleague in July is an hour out unless both parties meant the abbreviation literally. Broadcasters and airlines avoid the ambiguity by saying UTC. GMT itself is fixed at UTC+0 and does not shift; it is the UK's clocks that move away from it and back.
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 GMT switches to BST (UTC+1) from late March to late October. So the 3.5-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 GMT in IRST?
9:00 AM GMT is 12:30 PM IRST.
Is IRST ahead of GMT?
IRST is 3 hours 30 minutes ahead of GMT.
Which time zone does this use?
GMT is UTC+0 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.