Convert HST to ACDT
ACDT is 20 hours 30 minutes ahead of HST. HST is UTC−10 and ACDT is UTC+10:30.
Right now: HST · ACDT
Best time to schedule a meeting
Standard 9–5 working hours do not overlap at all between HST and ACDT. Someone has to take an early or late call — or use asynchronous communication instead.
| HST | ACDT | Suitable? |
|---|---|---|
| 9:00 AM | 5:30 AM (next day) | outside 9–5 |
| 10:00 AM | 6:30 AM (next day) | outside 9–5 |
| 11:00 AM | 7:30 AM (next day) | outside 9–5 |
| 12:00 PM | 8:30 AM (next day) | outside 9–5 |
| 1:00 PM | 9:30 AM (next day) | outside 9–5 |
| 2:00 PM | 10:30 AM (next day) | outside 9–5 |
| 3:00 PM | 11:30 AM (next day) | outside 9–5 |
| 4:00 PM | 12:30 PM (next day) | outside 9–5 |
| 5:00 PM | 1:30 PM (next day) | outside 9–5 |
HST to ACDT conversion table
| HST | ACDT |
|---|---|
| 12:00 AM | 8:30 PM |
| 1:00 AM | 9:30 PM |
| 2:00 AM | 10:30 PM |
| 3:00 AM | 11:30 PM |
| 4:00 AM | 12:30 AM (next day) |
| 5:00 AM | 1:30 AM (next day) |
| 6:00 AM | 2:30 AM (next day) |
| 7:00 AM | 3:30 AM (next day) |
| 8:00 AM | 4:30 AM (next day) |
| 9:00 AM | 5:30 AM (next day) |
| 10:00 AM | 6:30 AM (next day) |
| 11:00 AM | 7:30 AM (next day) |
| 12:00 PM | 8:30 AM (next day) |
| 1:00 PM | 9:30 AM (next day) |
| 2:00 PM | 10:30 AM (next day) |
| 3:00 PM | 11:30 AM (next day) |
| 4:00 PM | 12:30 PM (next day) |
| 5:00 PM | 1:30 PM (next day) |
| 6:00 PM | 2:30 PM (next day) |
| 7:00 PM | 3:30 PM (next day) |
| 8:00 PM | 4:30 PM (next day) |
| 9:00 PM | 5:30 PM (next day) |
| 10:00 PM | 6:30 PM (next day) |
| 11:00 PM | 7:30 PM (next day) |
About HST
Hawaii Standard Time (HST) is UTC−10. It is used in Hawaii, which does not observe daylight saving at all.
Hawaii–Aleutian Standard Time is UTC−10 and Hawaii does not observe daylight saving. That makes it the North American zone whose relationship to everywhere else changes twice a year without it doing anything: Hawaii is two hours behind Los Angeles in winter and three in summer. It is also far enough west that the working day barely overlaps with the US east coast at all.
About ACDT
Australian Central Daylight Time (ACDT) is UTC+10:30. It is used in Adelaide in summer.
Australian Central Daylight Time is UTC+10:30, what South Australia keeps from October to April. Darwin stays on ACST through the summer, so for those months two cities in the same nominal zone are an hour apart — the only reason to be precise about which of the two abbreviations a meeting invitation carries.
Does this gap change with the seasons?
Neither HST nor ACDT shifts with the seasons, so this 20.5-hour difference holds all year. That is unusual enough to be worth relying on: most cross-continental gaps move twice a year.
This is the reason scheduling systems store an IANA zone such as Region/City rather than an offset or an abbreviation: the zone knows its own rules and the offset does not.
Frequently asked questions
What time is 9:00 AM HST in ACDT?
9:00 AM HST is 5:30 AM ACDT (next day).
Is ACDT ahead of HST?
ACDT is 20 hours 30 minutes ahead of HST.
Which time zone does this use?
HST is UTC−10 and ACDT is UTC+10:30. Both abbreviations denote a single fixed offset, so this conversion never shifts with daylight saving — what changes is which abbreviation a place is using at the time.