How many hours is MST behind ACST?
As abbreviations, ACST is always 16.5 hours ahead of MST: MST is UTC−7 and ACST is UTC+9:30. To convert, add 16.5 hours.
Check which label you actually need: MST (Mountain Time is on MDT today). A time written with an abbreviation that is not in use is usually meant as the local time, so convert between the places instead: right now ACST is 15.5 hours ahead of MST.
When the MST to ACST time difference changes
For most of the year ACST is 15.5 hours ahead of MST. From 1 November to 31 December 2026, ACST is 16.5 hours ahead of MST instead, because the two places change their clocks on different dates. Meetings booked by the usual gap land an hour off in those weeks.
| Dates | ACST vs MST | Length |
|---|---|---|
| 8 March 2026 to 31 October 2026 | 15.5 hours ahead | 238 days |
| 1 November 2026 to 31 December 2026 | 16.5 hours ahead | 61 days |
| 1 January 2027 to 13 March 2027 | 16.5 hours ahead | 72 days |
| 14 March 2027 to 6 November 2027 | 15.5 hours ahead | 238 days |
| 7 November 2027 to 31 December 2027 | 16.5 hours ahead | 55 days |
Best time for a meeting between MST and ACST
- When ACST is 15.5 hours ahead of MST: no shared 09:00 to 17:00 hours; try 17:00 in MST (08:30 in ACST).
- When ACST is 16.5 hours ahead of MST: no shared 09:00 to 17:00 hours; try 17:00 in MST (09:30 in ACST).