If you didn’t get automatically enrolled in premium-free Part A (for example, because you’re still working and not yet getting Social Security or Railroad Retirement Board (RRB) benefits), you can sign up for premium-free Part A (if you’re eligible) any time during or after your Initial Enrollment Period begins. 

f you’re eligible for premium-free Part A, you can enroll in Part A any time after you’re first eligible for Medicare. Your Part A coverage will go back (retroactively) 6 months from when you enroll, but no earlier than the first month you’re eligible for Medicare. You can only sign up for Part B during the periods listed below. 

Remember, in most cases, if you don’t enroll in Part A (if you have to buy it) and Part B when you’re first eligible, your enrollment may be delayed and you may have to pay a late enrollment penalty. 

Are you eligible for Medicare Enrollment? 

Next : Medicare Enrollment Periods