Convert BST to ACST
ACST is 8 hours 30 minutes ahead of BST. BST is UTC+1 and ACST is UTC+9:30.
Right now: BST · ACST
Which BST is this?
BST names more than one zone. This page reads it as British Summer Time at UTC+1, which is the reading most converters take. There is one other: Bangladesh Standard Time at UTC+6, used in Bangladesh, all year.
The letters on a meeting invitation do not say which one is meant. If yours is not British Summer Time, the answer above is wrong, and not by a little:
| If BST means | Then |
|---|---|
| British Summer Time — assumed on this page | ACST is 8.5 hours ahead of BST |
| Bangladesh Standard Time | ACST is 3.5 hours ahead of BST |
The large converter sites disagree about this as well: search for a BST conversion and some of the results answer for one reading and some for another, none of them saying which they chose. Where it matters, ask which country the sender is in rather than which letters they typed.
Best time to schedule a meeting
Standard 9–5 working hours do not overlap at all between BST and ACST. Someone has to take an early or late call — or use asynchronous communication instead.
| BST | ACST | Suitable? |
|---|---|---|
| 9:00 AM | 5:30 PM | outside 9–5 |
| 10:00 AM | 6:30 PM | outside 9–5 |
| 11:00 AM | 7:30 PM | outside 9–5 |
| 12:00 PM | 8:30 PM | outside 9–5 |
| 1:00 PM | 9:30 PM | outside 9–5 |
| 2:00 PM | 10:30 PM | outside 9–5 |
| 3:00 PM | 11:30 PM | outside 9–5 |
| 4:00 PM | 12:30 AM (next day) | outside 9–5 |
| 5:00 PM | 1:30 AM (next day) | outside 9–5 |
BST to ACST conversion table
| BST | ACST |
|---|---|
| 12:00 AM | 8:30 AM |
| 1:00 AM | 9:30 AM |
| 2:00 AM | 10:30 AM |
| 3:00 AM | 11:30 AM |
| 4:00 AM | 12:30 PM |
| 5:00 AM | 1:30 PM |
| 6:00 AM | 2:30 PM |
| 7:00 AM | 3:30 PM |
| 8:00 AM | 4:30 PM |
| 9:00 AM | 5:30 PM |
| 10:00 AM | 6:30 PM |
| 11:00 AM | 7:30 PM |
| 12:00 PM | 8:30 PM |
| 1:00 PM | 9:30 PM |
| 2:00 PM | 10:30 PM |
| 3:00 PM | 11:30 PM |
| 4:00 PM | 12:30 AM (next day) |
| 5:00 PM | 1:30 AM (next day) |
| 6:00 PM | 2:30 AM (next day) |
| 7:00 PM | 3:30 AM (next day) |
| 8:00 PM | 4:30 AM (next day) |
| 9:00 PM | 5:30 AM (next day) |
| 10:00 PM | 6:30 AM (next day) |
| 11:00 PM | 7:30 AM (next day) |
About BST
British Summer Time (BST) is UTC+1. It is used in the UK from late March to late October.
British Summer Time is UTC+1, in force in the UK and Ireland from the last Sunday in March to the last Sunday in October. The abbreviation is ambiguous: BST also means Bangladesh Standard Time, UTC+6, five hours away. Within the UK it is the reason "GMT" is wrong for most of the year — the clocks are on BST from spring to autumn, and only the winter half of the year is actually GMT.
About ACST
Australian Central Standard Time (ACST) is UTC+9:30. It is used in Adelaide and Darwin in winter.
Australian Central Standard Time is UTC+9:30, half an hour behind the eastern states rather than a whole hour, which surprises people every time. South Australia moves to daylight saving in October and the Northern Territory does not, so Adelaide and Darwin share this offset for half the year and are an hour apart for the other half.
Does this gap change with the seasons?
This gap is seasonal. The abbreviations themselves are fixed offsets, but the region on BST switches to GMT (UTC+0) from late October to late March. So the 8.5-hour figure on this page is correct for the part of the year when both places are actually on these abbreviations, and changes by an hour outside it.
ACST does not shift, so the whole change comes from one side. A recurring meeting fixed in ACST will appear to move by an hour for everyone on the other side, twice a year, without anyone changing anything.
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 BST in ACST?
9:00 AM BST is 5:30 PM ACST.
Is ACST ahead of BST?
ACST is 8 hours 30 minutes ahead of BST.
Which time zone does this use?
BST is UTC+1 and ACST is UTC+9:30. 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.