Most colleges and universities in the United States divide academic years into two main semesters, states U.S. News & World Report. Typically, classes for the fall semester begin in late August, while spring semester classes begin between the middle and end of the following January.
The average length of each of the fall and spring semesters is between 15 and 18 weeks, notes U.S. News & World Report. Many universities and colleges also offer selected courses during the summer. Due to time constraints, the summer semester is shorter than either the fall or spring semesters, usually running for about half the time of either main semester.
While the two-semester system is standard for most schools, others subdivide their academic terms into three or four terms instead, explains U.S. News & World Report.