A Medicare supplement plan, often called Medigap, is designed to work alongside Original Medicare, not to expand it into a full health policy for every need. Its primary job is to help pay certain out-of-pocket costs left by Medicare Part A and Part B, such as deductibles, coinsurance, and copayments, depending on the plan letter.
It does not generally cover routine dental care, eye exams and eyeglasses, hearing aids, long-term custodial care, private-duty nursing, or most care received outside the United States. Prescription drugs are also not included in new supplement plan coverage; beneficiaries who want drug benefits typically enroll in a separate Medicare Part D plan.
Medicare Advantage works differently. Rather than supplementing Original Medicare, a Medicare Advantage plan is a private alternative through which you receive your Medicare-covered services. These plans often package Part A, Part B, and usually Part D into one policy, and may offer extra benefits for dental, vision, hearing, fitness, or transportation.
Those extras can be appealing, but plan rules matter: Medicare Advantage coverage may use provider networks, require referrals or prior authorization for some services, and set its own cost-sharing structure. You cannot use a supplement plan with Medicare Advantage.
The practical choice is between keeping Original Medicare and adding a supplement plan plus Part D, or enrolling in a Medicare Advantage plan. The right path depends on how you use care, the doctors and hospitals you prefer, your travel habits, and the predictability you want in your health expenses.