The Medicare Advantage Open Enrollment (OEP) takes place every year from January 1st – March 31st. Changes to Medicare plans made during this time will take effect the 1st of the following month of applying. For example, changes made in March will be effective April 1st. *The new OEP is replacing the Medicare Advantage Disenrollment Period, which used to be January 1 – February 14. *You must have already been enrolled in a Medicare Advantage plan to make changes during the Medicare Advantage Open Enrollment period.