If you're eligible for Medicare when you turn 65, you can sign up during your Initial Enrollment Period (IEP). This is a 7-month period that begins three months before the month you turn 65, includes the month you turn 65, and ends three months after the month you turn 65.
**Important: In some cases, if you don't sign up for Medicare Part B when you are first eligible, you will have to pay a late enrollment penalty for as long as you have Part B, and you could have a gap in your health coverage.
Once your Initial Enrollment Period ends, you may have a chance to sign up for Part A (if you have to buy it) and Part B during a Special Enrollment Period (SEP), but only if you meet certain requirements. If you're covered under a Group health plan based on current employment, you have a Special Enrollment Period to sign up for Part A and/or Part B at any time as long as you or your spouse (or family member if you are disabled) is working, and you're covered by a group health plan through the employer or union based on that work.
If you don't sign up for Part A (if you have to buy it) and/or Part B when you are first eligible, and you don't qualify for a Special Enrollment Period, you may have to wait to enroll until the Medicare General Enrollment Period which runs from January 1 to March 31. Coverage would not start until July 1st of that year. In most cases, you will have to pay a late enrollment penalty for as long as you have Part B if you sign up during the General Enrollment Period.