ACST to HST Time Converter
HST is 20 hours and 30 minutes behind ACST. Central Australia is currently on ACDT (UTC+10:30), and HST is UTC-10:00.
Best Time to Call Between ACST and HST
Both zones are inside normal business hours between 9:00 AM and 2:00 PM ACST — that's 12:30 PM to 5:30 PM HST. That's a 5-hour window.
both at work ACST only HST only neither — hours along the strip are ACST.
Common Times Converted
ACST on the left, HST on the right.
ACST to HST: Full 24-Hour Conversion Table
Shaded rows are working hours; the darker shade marks the hours when both zones are at work.
| ACST | HST | Working hours |
|---|---|---|
| 12:00 AM | 3:30 AM prev day | — |
| 1:00 AM | 4:30 AM prev day | — |
| 2:00 AM | 5:30 AM prev day | — |
| 3:00 AM | 6:30 AM prev day | — |
| 4:00 AM | 7:30 AM prev day | — |
| 5:00 AM | 8:30 AM prev day | — |
| 6:00 AM | 9:30 AM prev day | HST only |
| 7:00 AM | 10:30 AM prev day | HST only |
| 8:00 AM | 11:30 AM prev day | HST only |
| 9:00 AM | 12:30 PM prev day | Both zones |
| 10:00 AM | 1:30 PM prev day | Both zones |
| 11:00 AM | 2:30 PM prev day | Both zones |
| 12:00 PM | 3:30 PM prev day | Both zones |
| 1:00 PM | 4:30 PM prev day | Both zones |
| 2:00 PM | 5:30 PM prev day | ACST only |
| 3:00 PM | 6:30 PM prev day | ACST only |
| 4:00 PM | 7:30 PM prev day | ACST only |
| 5:00 PM | 8:30 PM prev day | — |
| 6:00 PM | 9:30 PM prev day | — |
| 7:00 PM | 10:30 PM prev day | — |
| 8:00 PM | 11:30 PM prev day | — |
| 9:00 PM | 12:30 AM | — |
| 10:00 PM | 1:30 AM | — |
| 11:00 PM | 2:30 AM | — |
What ACST and HST Actually Are
ACST — Australian Central Standard Time
Adelaide and Darwin. Standing at UTC+9:30 as written, and the region does change its clocks, so its live offset moves by an hour twice a year. The next change is on Sunday, April 4, 2027, to ACST. Adelaide moves to ACDT (UTC+10:30) in the southern summer; Darwin never changes.
The Central Australian half-hour offset dates from a 19th-century compromise between the colonies, and Adelaide observes daylight saving while Darwin, in the same zone, does not.
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
ACST 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 8 of the eight hours in a normal ACST 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.
This gap is not fixed
ACST changes its clocks and HST does not, so the difference between them moves by an hour twice a year. A recurring meeting set now will drift for one side from Sunday, April 4, 2027 unless someone resets it.
Nearly opposite sides of the clock
At 20 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 ACST
Cities on HST
Frequently Asked Questions
What is the time difference between ACST and HST?
HST is 20 hours and 30 minutes behind ACST. That is the live figure. Taken strictly as written, the gap between ACST and HST is 19 hours and 30 minutes — the two differ because at least one of these regions is currently on daylight saving.
What is 9:00 AM ACST in HST?
9:00 AM ACST is 12:30 PM the previous day HST.
What are the best hours to schedule a call between ACST and HST?
Between 9:00 AM and 2:00 PM ACST, which is 12:30 PM to 5:30 PM HST. Both sides are inside normal business hours through that window.
Does the difference between ACST and HST change during the year?
Yes. ACST observes daylight saving and HST does not, so the gap shifts by an hour at least twice a year. The next clock change is on Sunday, April 4, 2027.
Does ACST always mean Australian Central Standard Time?
Adelaide moves to ACDT (UTC+10:30) in the southern summer; Darwin never changes.
Does HST always mean Hawaii Standard Time?
Hawaii does not observe daylight saving, so this offset holds all year.