Highlighted rows fall within 09:00–18:00 in both places: 4 shared working hours.
How many hours is IST behind ACDT?
As abbreviations, ACDT is always 5 hours ahead of IST: IST is UTC+5:30 and ACDT is UTC+10:30. To convert, add 5 hours.
When the IST to ACDT time difference changes
For most of the year ACDT is 4 hours ahead of IST. From 4 October to 31 December 2026, ACDT is 5 hours ahead of IST 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 IST
Length
4 October 2026 to 31 December 2026
5 hours ahead
89 days
1 January 2027 to 3 April 2027
5 hours ahead
93 days
4 April 2027 to 2 October 2027
4 hours ahead
182 days
3 October 2027 to 31 December 2027
5 hours ahead
90 days
When IST and ACDT are both at work
When ACDT is 4 hours ahead of IST: 4 shared office hours, 09:00 to 13:00 in IST (13:00 to 17:00 in ACDT).
When ACDT is 5 hours ahead of IST: 3 shared office hours, 09:00 to 12:00 in IST (14:00 to 17:00 in ACDT).
Frequently asked questions about IST and ACDT time
How many hours ahead is ACDT of IST?
ACDT (UTC+10:30) is 5 hours ahead of IST (UTC+5:30).
Does the time difference between IST and ACDT change?
Yes. It is usually 4 hours ahead, but changes when one side moves its clocks: 5 hours ahead from 4 October to 31 December 2026; 5 hours ahead from 1 January to 3 April 2027.