You may sign up for Medicare Supplements, initially, a few months before your 65th birthday, effective the month you turn 65.
You must sign up for a Medicare Supplement before the 6th month after you turn 65, if you want to be guaranteed coverage.
Deadlines
October 15, 2018: Medicare Open Enrollment starts. This is the first day to enroll in a 2019 Medicare plan, whether you’re a current beneficiary or new to the program. During this time, you can sign up for Medicare Advantage (Part C) or Part D, or you can change your coverage.
December 7, 2018: 2019 Medicare Open Enrollment ends.
January 1, 2019: This is the first day your coverage starts for your new plan; any previous changes take effect.
January 1 – February 14, 2019: Medicare Advantage Disenrollment Period. Medicare Advantage enrollees can switch back to original Medicare. You can also sign up for Medicare Part D plans in this period if you drop an MA plan and switch to original Medicare without drug coverage.
Medicare and Dental coverage