Fall Open Enrollment occurs each year from October 15 to December 7. During Fall Open Enrollment, people with Medicare can make changes to their existing Medicare coverage. While you can make as many changes as you want to your Medicare coverage during Fall Open Enrollment, the last change you make during this time will take effect on January 1, 2014. To avoid enrollment problems, it’s best to call 800-MEDICARE when making any changes to your Medicare health and/or drug coverage.