The Annual Enrollment Period (AEP) runs October 15 through December 7 each year, when anyone with Medicare can join, switch, or drop a Medicare Advantage plan. The Medicare Advantage Open Enrollment Period (OEP) runs January 1 through March 31, but only applies if you're already enrolled in a Medicare Advantage plan and want to make one change.
Outside those windows, you may still qualify for a Special Enrollment Period if you've moved, lost other coverage, or had certain other life changes.