Time zone · Oceania
ACST
Australian Central Standard Time
Australian Central Standard Time (ACST) sits at UTC+09:30 and covers three mainland Australian zones — Adelaide, Broken Hill, and Darwin. It's one of the world's rare half-hour offset regions, splitting the gap between standard eastern and western Australia, making it a fascinating timezone quirk for global teams trying to slot meetings at the "quarter-to-ten" mark. Two of its three member zones observe daylight saving (Adelaide and Broken Hill), while Darwin stays on standard time year-round — so if you're scheduling with Central Australia, always double-check who's springing forward.
Sunday, May 31, 2026
Current offset
UTC+09:30
Standard · ACST
Daylight saving
Not active
Returns 4 Oct 2026
IANA zones
3
2 observe DST, 1 doesn't
DST offset
UTC+10:30
ACDT · +1h
About ACST
Standard time, with a summer shift.
Australian Central Standard Time (ACST) sits at UTC+09:30 and covers three mainland Australian zones — Adelaide, Broken Hill, and Darwin. It's one of the world's rare half-hour offset regions, splitting the gap between standard eastern and western Australia, making it a fascinating timezone quirk for global teams trying to slot meetings at the "quarter-to-ten" mark. Two of its three member zones observe daylight saving (Adelaide and Broken Hill), while Darwin stays on standard time year-round — so if you're scheduling with Central Australia, always double-check who's springing forward.
DST schedule · ACST · ACDT
2026 Sunday · clocks spring forward
Clocks spring forward by one hour · in 4 months.
Affects 2 of 3 zones — the rest stay on ACST year-round.
One year, two clocks
IANA zones · the technical identifiers
The 3 zones that resolve to ACST.
For software, always store the IANA identifier — never the abbreviation alone. The database keeps these zones distinct because their rules can, and historically did, diverge.
Where ACST is used
One country.
Frequently asked questions
Common questions about ACST, daylight saving, and how to handle it in software. Can't find what you need? Email [email protected].
- Why does Australia use a half-hour offset?
- Australia spans three standard time zones, and the UTC+09:30 offset fills the geographic gap neatly between Western (UTC+08:00) and Eastern (UTC+10:00) — a practical compromise from the 19th century.
- Which ACST places observe daylight saving?
- Adelaide and Broken Hill do — they switch to ACDT (UTC+10:30) in summer. Darwin (NT) does not, so during DST season, there's a 1-hour spread within the ACST code itself.
- When does Adelaide observe DST?
- Daylight saving time for zones in South Australia ends on the first Sunday in April and starts again on the first Sunday in October, adding extra evening daylight during the southern hemisphere summer.
- Is Broken Hill in the same timezone as the rest of New South Wales?
- Not exactly — Broken Hill follows ACST with South Australia because it's closer to Adelaide than Sydney. It even shares South Australia's phone codes and relies on Adelaide-based TV and radio stations.
- How does ACST relate to international business hours?
- The UTC+09:30 offset places ACST ahead of most of Asia-Pacific during their workday. It aligns closely with Japan and South Korea at UTC+09:00, making ACST an easy slot for morning conference calls across the region.
- Why doesn't Darwin observe DST?
- Darwin is close to the equator, where daylight hours vary minimally year-round, so DST offers little benefit. Queensland also opted out of DST for similar practical reasons.
- What makes ACST unique globally?
- Half-hour offset timezones are rare worldwide, and ACST is one of the most well-known examples alongside India's IST (UTC+05:30) and Myanmar (UTC+06:30). It's a fun fact you've got at the 'quarter-to-ten' offset!
- Why do only 3 zones use ACST?
- ACST is specific to Central Australia. While it covers a small number of official zones, it literally spans the continent — from South Australia's coast (Adelaide/Broken Hill) through to the tropical Northern Territory (Darwin).
Free · Developer API
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