ACST to HST
-19h 30mACST
ACSTSOURCEHST
HSTGreen rows indicate typical business hours (9 AM - 5 PM)
ACST and HST on the World Map
The map below highlights the ACST (Australian Central Standard Time) and HST (Hawaii Standard Time) timezone regions across the globe.
ACST – Australian Central Standard Time
UTC+09:30Australian Central Standard Time (ACST, UTC+09:30) covers South Australia and the Northern Territory, on a half-hour offset.
- •ACST uses a half-hour offset: UTC+09:30.
- •South Australia moves to ACDT (UTC+10:30) in summer; the Northern Territory does not.
- •Adelaide and Darwin are 30 minutes apart during daylight saving, level in winter.
- •Adelaide is one of the few major cities on a 30-minute offset.
HST – Hawaii Standard Time
UTC-10:00Hawaii Standard Time (HST) is the time zone for the Hawaiian Islands, 10 hours behind UTC.
- •Hawaii does not observe daylight saving time.
- •HST is 5 hours behind EST in winter and 6 hours behind EDT in summer.
- •Hawaii is one of only two US states that don't observe DST (the other is Arizona).
Understanding the -19h 30m Gap: ACST vs HST
ACST runs on Australian Central Standard Time (ACST) at UTC+09:30. HST runs on Hawaii Standard Time (HST) at UTC-10:00. That puts ACST 19 hours 30 minutes behind HST — a difference of -19h 30m at the current offsets.
In practice, when it is 9:00 AM in ACST it is 1:30 PM in HST on the previous day. Midnight in ACST is 4:30 AM in HST. Neither zone observes daylight saving time, so the offset between them stays constant all year.
ACST to HST time conversion table
| ACST (ACST) | HST (HST) | Day |
|---|---|---|
| 12:00 AM | 4:30 AM | previous day |
| 6:00 AM | 10:30 AM | previous day |
| 7:00 AM | 11:30 AM | previous day |
| 8:00 AM | 12:30 PM | previous day |
| 9:00 AM | 1:30 PM | previous day |
| 12:00 PM | 4:30 PM | previous day |
| 3:00 PM | 7:30 PM | previous day |
| 5:00 PM | 9:30 PM | previous day |
| 6:00 PM | 10:30 PM | previous day |
| 9:00 PM | 1:30 AM | same day |
Why people convert ACST to HST time
- Scheduling a call from ACST to HST: a 10:00 AM start in ACST lands at 2:30 PM in HST the previous day, so you can confirm the slot without doing the arithmetic yourself.
- Handling a -19h 30m gap: ACST and HST have no overlap inside a normal 9-to-5 day, so real-time meetings need an early-morning or late-evening slot on one side. 9:00 AM in HST is 1:30 PM in ACST.
- Booking travel or deliveries: tracking HST local time against ACST keeps pickup windows and arrival estimates honest across the -19h 30m offset.
- Always state the zone abbreviation, not just the hour. "3:00 PM ACST" is unambiguous; "3 PM" across a -19h 30m gap is not.
- With a -19h 30m gap there is no shared 9-to-5 window, so alternate the early start: one week ACST takes the early slot, the next week HST does.
About ACST (Australian Central Standard Time)
Australian Central Standard Time (ACST) is the half-hour offset of UTC+09:30 used across South Australia and the Northern Territory, taking in Adelaide and Darwin. South Australia moves to Australian Central Daylight Time (ACDT, UTC+10:30) from the first Sunday in October to the first Sunday in April, but the Northern Territory does not observe daylight saving — so Adelaide and Darwin sit 30 minutes apart in summer and level with each other in winter. The half-hour offset means Adelaide is 30 minutes behind Sydney in winter and level with it during daylight saving, which regularly catches out travellers and meeting planners.
About HST (Hawaii Standard Time)
Hawaii Standard Time (HST) is used in the state of Hawaii and does not observe daylight saving time. This makes HST one of the most consistent time zones in the US. The Hawaiian Islands are among the last places on Earth to see a new calendar day.
Best time to call between ACST and HST
With a -19h 30m offset there is no overlap inside a normal 9 AM – 5 PM day. HST opens at 9:00 AM HST, which is 1:30 PM in ACST, so real-time calls need an early-morning or late-evening slot on one side.
Business hours overlap
ACST and HST have no shared working hours because of the -19h 30m gap. Teams need to alternate early starts or rely on asynchronous handovers.
ACST is 19 hours 30 minutes behind HST (ACST UTC+09:30 → HST UTC-10:00). There is no shared 9-to-5 window, so plan around an early or late slot. Remember to re-check around daylight-saving transitions.
🕐 Daylight Saving Time Info
ACST
❄ Currently in Standard Time
Standard: UTC+09:30 · DST: UTC+10:30
Clocks spring forward on Sat, Oct 3, 2026
HST
Does not observe DST
Learn More About Time
Dive deeper into the fascinating world of timekeeping, time zones, and how they shape our global society:
Frequently Asked Questions
What is the time difference between ACST and HST?
ACST (ACST, UTC+09:30) is 19 hours 30 minutes behind HST (HST, UTC-10:00). The gap is currently -19h 30m.
How do I convert ACST time to HST time?
Add -19h 30m to ACST local time. For example, 9:00 AM in ACST is 1:30 PM in HST (previous day).
What time is it in HST right now?
HST uses HST at UTC-10:00. Use the live converter at the top of this page — it updates in real time and already accounts for the -19h 30m offset from ACST.
What is the best time to call HST from ACST?
There is no shared working-hours window because of the -19h 30m gap. The closest option is 1:00 PM in ACST, which is 5:30 PM in HST.
Which is behind, ACST or HST?
ACST is 19 hours 30 minutes behind HST. When it is 12:00 PM in ACST it is 4:30 PM in HST.
Does daylight saving time affect the ACST–HST difference?
Neither zone observes daylight saving time, so the -19h 30m offset between ACST and HST is fixed all year.
Which other cities share ACST's time zone?
ACST also covers Adelaide, Darwin, Alice Springs, Mount Gambier.
Which countries use ACST, ACST's zone?
ACST is used in Australia (South Australia, Northern Territory).
Is there a day difference between ACST and HST?
Sometimes. The -19h 30m gap is large enough that 8:00 PM or later in ACST already falls on the in HST.
What is the time difference between ACST and HST?
HST is -19h 30m from ACST.
What timezone is ACST in?
ACST operates on its local timezone.
What timezone is HST in?
HST operates on its local timezone.
Which countries use ACST (Australian Central Standard Time)?
ACST is used in Australia (South Australia, Northern Territory).
Does ACST observe daylight saving time?
Yes, ACST switches to ACDT during summer months.
What are some interesting facts about ACST?
ACST uses a half-hour offset: UTC+09:30. South Australia moves to ACDT (UTC+10:30) in summer; the Northern Territory does not.
Which cities are in the HST timezone?
Major cities in the HST timezone include Honolulu, Hilo, Kailua, Pearl City, Kapolei.
What is the UTC offset for HST?
Hawaii Standard Time (HST) is at UTC-10:00.
What should I know about the HST timezone?
Hawaii does not observe daylight saving time. HST is 5 hours behind EST in winter and 6 hours behind EDT in summer.
When is it midnight in ACST, what time is it in HST?
When it is 12:00 AM (midnight) in ACST (ACST), it is -19h 30m later in HST (HST).
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See every conversion from ACST →·See every conversion from HST →