When Does Medicare Become Primary? 
Medicare is almost always the primary insurance . Where there is often confusion on this subject is when a person remains working beyond the age of 65 . If a person continues working beyond age 65 and remains covered under an employer health insurance policy , the individual does not have to sign up for Medicare . It is critical to contact your employer 's Human Resource department or your local Social Security office to find out the details . In most cases , the company will write a letter to the Social Security Administration that states the person had company coverage until a certain date . Once the person retires , leaves the company , or no longer has employer coverage , they can then sign up for Medicare at that time without having to worry about the penalties . 