IST to HST Time Converter
HST is 15 hours and 30 minutes behind IST. IST is UTC+5:30, and HST is UTC-10:00.
Best Time to Call Between IST 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 2:00 PM IST, which is 3:30 PM to 10:30 PM HST.
both at work IST only HST only neither — hours along the strip are IST.
Common Times Converted
IST on the left, HST on the right.
IST to HST: Full 24-Hour Conversion Table
Shaded rows are working hours; the darker shade marks the hours when both zones are at work.
| IST | HST | Working hours |
|---|---|---|
| 12:00 AM | 8:30 AM prev day | — |
| 1:00 AM | 9:30 AM prev day | HST only |
| 2:00 AM | 10:30 AM prev day | HST only |
| 3:00 AM | 11:30 AM prev day | HST only |
| 4:00 AM | 12:30 PM prev day | HST only |
| 5:00 AM | 1:30 PM prev day | HST only |
| 6:00 AM | 2:30 PM prev day | HST only |
| 7:00 AM | 3:30 PM prev day | HST only |
| 8:00 AM | 4:30 PM prev day | HST only |
| 9:00 AM | 5:30 PM prev day | IST only |
| 10:00 AM | 6:30 PM prev day | IST only |
| 11:00 AM | 7:30 PM prev day | IST only |
| 12:00 PM | 8:30 PM prev day | IST only |
| 1:00 PM | 9:30 PM prev day | IST only |
| 2:00 PM | 10:30 PM prev day | IST only |
| 3:00 PM | 11:30 PM prev day | IST only |
| 4:00 PM | 12:30 AM | IST only |
| 5:00 PM | 1:30 AM | — |
| 6:00 PM | 2:30 AM | — |
| 7:00 PM | 3:30 AM | — |
| 8:00 PM | 4:30 AM | — |
| 9:00 PM | 5:30 AM | — |
| 10:00 PM | 6:30 AM | — |
| 11:00 PM | 7:30 AM | — |
What IST and HST Actually Are
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.
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
IST 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 7 of the eight hours in a normal IST 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 15 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 IST
Cities on HST
Frequently Asked Questions
What is the time difference between IST and HST?
HST is 15 hours and 30 minutes behind IST.
What is 9:00 AM IST in HST?
9:00 AM IST is 5:30 PM the previous day HST.
What are the best hours to schedule a call between IST 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 2:00 PM IST, which is 3:30 PM to 10:30 PM HST.
Does the difference between IST and HST change during the year?
No. Neither region changes its clocks, so this gap is fixed all year round.
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.
Does HST always mean Hawaii Standard Time?
Hawaii does not observe daylight saving, so this offset holds all year.