How many hours is MST behind ACDT?
As abbreviations, ACDT is always 17.5 hours ahead of MST: MST is UTC−7 and ACDT is UTC+10:30. To convert, add 17.5 hours.
When the MST to ACDT time difference changes
For most of the year ACDT is 15.5 hours ahead of MST. From 1 November to 31 December 2026, ACDT is 17.5 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 | ACDT vs MST | Length |
|---|---|---|
| 1 November 2026 to 31 December 2026 | 17.5 hours ahead | 61 days |
| 1 January 2027 to 13 March 2027 | 17.5 hours ahead | 72 days |
| 14 March 2027 to 3 April 2027 | 16.5 hours ahead | 21 days |
| 4 April 2027 to 2 October 2027 | 15.5 hours ahead | 182 days |
| 3 October 2027 to 6 November 2027 | 16.5 hours ahead | 35 days |
| 7 November 2027 to 31 December 2027 | 17.5 hours ahead | 55 days |
Calling hours for MST and ACDT
- When ACDT is 15.5 hours ahead of MST: no shared 09:00 to 17:00 hours; try 17:00 in MST (08:30 in ACDT).
- When ACDT is 17.5 hours ahead of MST: no shared 09:00 to 17:00 hours; one side has to take the call outside office hours.
- When ACDT is 16.5 hours ahead of MST: no shared 09:00 to 17:00 hours; try 17:00 in MST (09:30 in ACDT).