Did you have employer insurance through a current job or your spouse’s job at the time you became eligible for Medicare?

If yes:

    You may be eligible for a Special Enrollment Period, which means you can enroll in Medicare without penalty at any time while you have group health coverage and for eight months after you lose your group health coverage or you (or your spouse) stop working, whichever comes first.
    Note: If you are under 65, have Medicare due to disability and have health insurance through your domestic partner’s current employer, you may also be entitled to a Special Enrollment Period if there are at least 100 employees at your domestic partner’s place of work.

If no:

    You can apply for Medicare during the General Enrollment Period, between January 1 and March 31 of each year. Your coverage will start the following July and you will have to pay a Part B premium penalty.