IBA follows the Academic Calendar of the University of Dhaka.  
The  difference is that at IBA there are two semesters every year.  
The early semester starts in February and runs up to June. The other semester starts in the month of August and continues till December. Some specific courses, for unavoidable reasons, may continue for one or two weeks after the official end of the semester. This, however, creates no session jam, because, there is a gap of one month between two consecutive semesters.