The academic calendar is based on the semester system, which divides the academic year, lasting from mid-August to early May, into two 15-week semesters (fall and spring) and the summer. The fall semester ends in early December and the spring term begins in early January. The summer, which lasts from mid-May to August, is divided into a number of sessions: a 12-week session, a 3-week "mini-semester" in May, a nine-week session in June and July, and two four-week sessions in June and July, respectively.[33] The schools of medicine and dentistry follow an academic calendar beginning in July and ending in late May/early June.[34][35]