HST to ACST
+19h 30mHST
HSTSOURCEACST
ACSTGreen rows indicate typical business hours (9 AM - 5 PM)
HST and ACST on the World Map
The map below highlights the HST (Hawaii Standard Time) and ACST (Australian Central Standard Time) timezone regions across the globe.
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).
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 vs ACST: Offsets, DST and Best Call Times
HST runs on Hawaii Standard Time (HST) at UTC-10:00. ACST runs on Australian Central Standard Time (ACST) at UTC+09:30. That puts HST 19 hours 30 minutes ahead of ACST — a difference of +19h 30m at the current offsets.
In practice, when it is 9:00 AM in HST it is 4:30 AM in ACST on the next day. Midnight in HST is 7:30 PM in ACST. Neither zone observes daylight saving time, so the offset between them stays constant all year.
HST to ACST time conversion table
| HST (HST) | ACST (ACST) | Day |
|---|---|---|
| 12:00 AM | 7:30 PM | same day |
| 6:00 AM | 1:30 AM | next day |
| 7:00 AM | 2:30 AM | next day |
| 8:00 AM | 3:30 AM | next day |
| 9:00 AM | 4:30 AM | next day |
| 12:00 PM | 7:30 AM | next day |
| 3:00 PM | 10:30 AM | next day |
| 5:00 PM | 12:30 PM | next day |
| 6:00 PM | 1:30 PM | next day |
| 9:00 PM | 4:30 PM | next day |
Why people convert HST to ACST time
- Scheduling a call from HST to ACST: a 10:00 AM start in HST lands at 5:30 AM in ACST the next day, so you can confirm the slot without doing the arithmetic yourself.
- Handling a +19h 30m gap: HST and ACST 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 ACST is 4:30 AM in HST.
- Watching a live event or market open: HST viewers need 4:30 AM in ACST to catch a 9:00 AM start there, and 4:30 AM if the event is anchored to HST.
- Always state the zone abbreviation, not just the hour. "3:00 PM HST" 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 HST takes the early slot, the next week ACST does.
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.
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.
Best time to call between HST and ACST
With a +19h 30m offset there is no overlap inside a normal 9 AM – 5 PM day. ACST opens at 9:00 AM ACST, which is 4:30 AM in HST, so real-time calls need an early-morning or late-evening slot on one side.
Business hours overlap
HST and ACST have no shared working hours because of the +19h 30m gap. Teams need to alternate early starts or rely on asynchronous handovers.
HST is 19 hours 30 minutes ahead of ACST (HST UTC-10:00 → ACST UTC+09:30). 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
HST
Does not observe DST
ACST
❄ Currently in Standard Time
Standard: UTC+09:30 · DST: UTC+10:30
Clocks spring forward on Sat, Oct 3, 2026
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 HST and ACST?
HST (HST, UTC-10:00) is 19 hours 30 minutes ahead of ACST (ACST, UTC+09:30). The gap is currently +19h 30m.
How do I convert HST time to ACST time?
Add +19h 30m to HST local time. For example, 9:00 AM in HST is 4:30 AM in ACST (next day).
What time is it in ACST right now?
ACST uses ACST at UTC+09:30. Use the live converter at the top of this page — it updates in real time and already accounts for the +19h 30m offset from HST.
What is the best time to call ACST from HST?
There is no shared working-hours window because of the +19h 30m gap. The closest option is 1:00 PM in HST, which is 8:30 AM in ACST.
Which is ahead, HST or ACST?
HST is 19 hours 30 minutes ahead of ACST. When it is 12:00 PM in HST it is 7:30 AM in ACST.
Does daylight saving time affect the HST–ACST difference?
Neither zone observes daylight saving time, so the +19h 30m offset between HST and ACST is fixed all year.
Which other cities share HST's time zone?
HST also covers Honolulu, Hilo, Kailua, Pearl City, Kapolei.
Which countries use HST, HST's zone?
HST is used in United States (Hawaii).
Is there a day difference between HST and ACST?
Sometimes. The +19h 30m gap is large enough that 8:00 PM or later in HST already falls on the next day in ACST.
What is the time difference between HST and ACST?
ACST is +19h 30m from HST.
What timezone is HST in?
HST operates on its local timezone.
What timezone is ACST in?
ACST operates on its local timezone.
Which countries use HST (Hawaii Standard Time)?
HST is used in United States (Hawaii).
Does HST observe daylight saving time?
No, HST does not observe daylight saving time and remains at UTC-10:00 year-round.
What are some interesting facts about HST?
Hawaii does not observe daylight saving time. HST is 5 hours behind EST in winter and 6 hours behind EDT in summer.
Which cities are in the ACST timezone?
Major cities in the ACST timezone include Adelaide, Darwin, Alice Springs, Mount Gambier.
What is the UTC offset for ACST?
Australian Central Standard Time (ACST) is at UTC+09:30. During daylight saving time, it shifts to ACDT.
What should I know about the ACST timezone?
ACST uses a half-hour offset: UTC+09:30. South Australia moves to ACDT (UTC+10:30) in summer; the Northern Territory does not.
When is it midnight in HST, what time is it in ACST?
When it is 12:00 AM (midnight) in HST (HST), it is +19h 30m later in ACST (ACST).
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See every conversion from HST →·See every conversion from ACST →