IRST to IST Time Converter
IST is 2 hours ahead of IRST. IRST is UTC+3:30, and IST is UTC+5:30.
Best Time to Call Between IRST and IST
Both zones are inside normal business hours between 9:00 AM and 3:00 PM IRST — that's 11:00 AM to 5:00 PM IST. That's a 6-hour window.
both at work IRST only IST only neither — hours along the strip are IRST.
Common Times Converted
IRST on the left, IST on the right.
IRST to IST: Full 24-Hour Conversion Table
Shaded rows are working hours; the darker shade marks the hours when both zones are at work.
| IRST | IST | Working hours |
|---|---|---|
| 12:00 AM | 2:00 AM | — |
| 1:00 AM | 3:00 AM | — |
| 2:00 AM | 4:00 AM | — |
| 3:00 AM | 5:00 AM | — |
| 4:00 AM | 6:00 AM | — |
| 5:00 AM | 7:00 AM | — |
| 6:00 AM | 8:00 AM | — |
| 7:00 AM | 9:00 AM | IST only |
| 8:00 AM | 10:00 AM | IST only |
| 9:00 AM | 11:00 AM | Both zones |
| 10:00 AM | 12:00 PM | Both zones |
| 11:00 AM | 1:00 PM | Both zones |
| 12:00 PM | 2:00 PM | Both zones |
| 1:00 PM | 3:00 PM | Both zones |
| 2:00 PM | 4:00 PM | Both zones |
| 3:00 PM | 5:00 PM | IRST only |
| 4:00 PM | 6:00 PM | IRST only |
| 5:00 PM | 7:00 PM | — |
| 6:00 PM | 8:00 PM | — |
| 7:00 PM | 9:00 PM | — |
| 8:00 PM | 10:00 PM | — |
| 9:00 PM | 11:00 PM | — |
| 10:00 PM | 12:00 AM next day | — |
| 11:00 PM | 1:00 AM next day | — |
What IRST and IST 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.
IST — India Standard Time
Mumbai, Delhi, Bengaluru, Chennai, Kolkata, Hyderabad — and Colombo. Standing at UTC+5:30 as written, and the region does not change its clocks, so that offset holds all year. IST also stands for Irish Standard Time (UTC+1) and Israel Standard Time (UTC+2). This page covers the Indian one, which is by far the most searched.
India runs a single time zone across a country wide enough for two, which is why sunrise in the north-east can come nearly two hours before Mumbai's. Proposals for a second zone resurface regularly and have never been adopted.
What This Means in Practice
Expect times on the half hour
Both IRST and IST sit 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.
A gap you can rely on
Neither region changes its clocks, so this difference holds every day of the year. A recurring meeting booked once stays correct — worth knowing, because most cross-border pairs cannot say that.
Close enough to share a working day
At only 2 hours apart, the two working days overlap almost completely. Scheduling is barely constrained by the difference.
Major Cities in Each Zone
Cities on IRST
Cities on IST
Frequently Asked Questions
What is the time difference between IRST and IST?
IST is 2 hours ahead of IRST.
What is 9:00 AM IRST in IST?
9:00 AM IRST is 11:00 AM IST.
What are the best hours to schedule a call between IRST and IST?
Between 9:00 AM and 3:00 PM IRST, which is 11:00 AM to 5:00 PM IST. Both sides are inside normal business hours through that window.
Does the difference between IRST and IST change during the year?
No. Neither region changes its clocks, so this gap is fixed all year round.
Does IRST always mean Iran Standard Time?
Iran abolished daylight saving in 2022, so the half-hour offset now holds all year.
Does IST always mean India Standard Time?
IST also stands for Irish Standard Time (UTC+1) and Israel Standard Time (UTC+2). This page covers the Indian one, which is by far the most searched.