Medicare Advantage Plan Enrollment When You Can Enroll in Medicare Advantage (MA-MAPD) To enroll in a Medicare Advantage Plan, you must be enrolled in Medicare Parts A and BYou can typically enroll in Medicare Advantage during the following periods: Initial Enrollment Period (IEP): Once you have enrolled in Medicare Parts A and B, you can also enroll in a Medicare Advantage Plan. Part B Special Enrollment Period (SEP): If you use the Part B SEP, you can enroll in an MA Plan after you have signed up for Part A and B coverage. General Enrollment Period (GEP): If you enroll in Medicare using the GEP January-March, your coverage will become effective July 1. You can enroll in a Medicare Advantage Plan in April through June. Fall Open Enrollment: This is the period from October 15 to December 7 every year when you can change your Medicare coverage, including by enrolling in a Medicare Advantage Plan.