HST to IRST Time Converter
IRST is 13 hours and 30 minutes ahead of HST. HST is UTC-10:00, and IRST is UTC+3:30.
Best Time to Call Between HST and IRST
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 6:00 PM to 10:00 PM HST, which is 7:30 AM to 11:30 AM IRST.
both at work HST only IRST only neither — hours along the strip are HST.
Common Times Converted
HST on the left, IRST on the right.
HST to IRST: Full 24-Hour Conversion Table
Shaded rows are working hours; the darker shade marks the hours when both zones are at work.
| HST | IRST | Working hours |
|---|---|---|
| 12:00 AM | 1:30 PM | IRST only |
| 1:00 AM | 2:30 PM | IRST only |
| 2:00 AM | 3:30 PM | IRST only |
| 3:00 AM | 4:30 PM | IRST only |
| 4:00 AM | 5:30 PM | — |
| 5:00 AM | 6:30 PM | — |
| 6:00 AM | 7:30 PM | — |
| 7:00 AM | 8:30 PM | — |
| 8:00 AM | 9:30 PM | — |
| 9:00 AM | 10:30 PM | HST only |
| 10:00 AM | 11:30 PM | HST only |
| 11:00 AM | 12:30 AM next day | HST only |
| 12:00 PM | 1:30 AM next day | HST only |
| 1:00 PM | 2:30 AM next day | HST only |
| 2:00 PM | 3:30 AM next day | HST only |
| 3:00 PM | 4:30 AM next day | HST only |
| 4:00 PM | 5:30 AM next day | HST only |
| 5:00 PM | 6:30 AM next day | — |
| 6:00 PM | 7:30 AM next day | — |
| 7:00 PM | 8:30 AM next day | — |
| 8:00 PM | 9:30 AM next day | IRST only |
| 9:00 PM | 10:30 AM next day | IRST only |
| 10:00 PM | 11:30 AM next day | IRST only |
| 11:00 PM | 12:30 PM next day | IRST only |
What HST and IRST Actually Are
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.
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.
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 6 of the eight hours in a normal HST working day, the equivalent IRST 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 HST
Cities on IRST
Frequently Asked Questions
What is the time difference between HST and IRST?
IRST is 13 hours and 30 minutes ahead of HST.
What is 9:00 AM HST in IRST?
9:00 AM HST is 10:30 PM IRST.
What are the best hours to schedule a call between HST and IRST?
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 6:00 PM to 10:00 PM HST, which is 7:30 AM to 11:30 AM IRST.
Does the difference between HST and IRST change during the year?
No. Neither region changes its clocks, so this gap is fixed all year round.
Does HST always mean Hawaii Standard Time?
Hawaii does not observe daylight saving, so this offset holds all year.
Does IRST always mean Iran Standard Time?
Iran abolished daylight saving in 2022, so the half-hour offset now holds all year.