IRST to HST Time Converter
HST is 13 hours and 30 minutes behind IRST. IRST is UTC+3:30, and HST is UTC-10:00.
Best Time to Call Between IRST and HST
Standard 9-to-5 hours in these two zones never overlap, so someone has to take the call outside their working day. The most workable window is 7:00 AM to 12:00 PM IRST, which is 5:30 PM to 10:30 PM HST.
both at work IRST only HST only neither — hours along the strip are IRST.
Common Times Converted
IRST on the left, HST on the right.
IRST to HST: Full 24-Hour Conversion Table
Shaded rows are working hours; the darker shade marks the hours when both zones are at work.
| IRST | HST | Working hours |
|---|---|---|
| 12:00 AM | 10:30 AM prev day | HST only |
| 1:00 AM | 11:30 AM prev day | HST only |
| 2:00 AM | 12:30 PM prev day | HST only |
| 3:00 AM | 1:30 PM prev day | HST only |
| 4:00 AM | 2:30 PM prev day | HST only |
| 5:00 AM | 3:30 PM prev day | HST only |
| 6:00 AM | 4:30 PM prev day | HST only |
| 7:00 AM | 5:30 PM prev day | — |
| 8:00 AM | 6:30 PM prev day | — |
| 9:00 AM | 7:30 PM prev day | IRST only |
| 10:00 AM | 8:30 PM prev day | IRST only |
| 11:00 AM | 9:30 PM prev day | IRST only |
| 12:00 PM | 10:30 PM prev day | IRST only |
| 1:00 PM | 11:30 PM prev day | IRST only |
| 2:00 PM | 12:30 AM | IRST only |
| 3:00 PM | 1:30 AM | IRST only |
| 4:00 PM | 2:30 AM | IRST only |
| 5:00 PM | 3:30 AM | — |
| 6:00 PM | 4:30 AM | — |
| 7:00 PM | 5:30 AM | — |
| 8:00 PM | 6:30 AM | — |
| 9:00 PM | 7:30 AM | — |
| 10:00 PM | 8:30 AM | — |
| 11:00 PM | 9:30 AM | HST only |
What IRST and HST 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.
HST — Hawaii Standard Time
Honolulu and the rest of Hawaii. Standing at UTC-10:00 as written, and the region does not change its clocks, so that offset holds all year. Hawaii does not observe daylight saving, so this offset holds all year.
Hawaii dropped daylight saving in 1967 and never resumed it. Being close to the equator, its daylight barely varies across the year, so there is little to gain.
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.
The date changes mid-working-day
For 5 of the eight hours in a normal IRST working day, the equivalent HST time falls on a different calendar date. Anything scheduled in that stretch needs the date checked as well as the time, or a Tuesday call quietly becomes a Wednesday one at the other end.
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.
Nearly opposite sides of the clock
At 13 hours and 30 minutes apart, one side's morning is the other side's night. Handing work over at the end of a shift usually beats trying to get both parties in the same call.
Major Cities in Each Zone
Cities on IRST
Cities on HST
Frequently Asked Questions
What is the time difference between IRST and HST?
HST is 13 hours and 30 minutes behind IRST.
What is 9:00 AM IRST in HST?
9:00 AM IRST is 7:30 PM the previous day HST.
What are the best hours to schedule a call between IRST and HST?
Standard business hours in these two zones do not overlap at all, so one side has to work outside the 9-to-5. The most workable window is 7:00 AM to 12:00 PM IRST, which is 5:30 PM to 10:30 PM HST.
Does the difference between IRST and HST 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 HST always mean Hawaii Standard Time?
Hawaii does not observe daylight saving, so this offset holds all year.