The Medicare Advantage Open Enrollment (OEP) takes place every year from January 1^st – March 31^st. Changes to Medicare plans made during this time will take effect the 1^st of the following month of applying. For example, changes made in March will be effective April 1^st. *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.