You About**
Original Medicare Parts A and B operates as a fee-for-service program. You see any doctor, hospital, or specialist in the United States who accepts Medicare. Approximately 90% of physicians accept Medicare. There are no referrals required for specialist visits. There are no network boundaries. The trade-off is cost exposure. Original Medicare does not have an annual out-of-pocket maximum. The 20% coinsurance on Part B services doctor visits, outpatient procedures applies indefinitely. A serious illness with multiple hospitalizations can result in very large out-of-pocket bills. To address this, most Original Medicare enrollees purchase a Medicare Supplement Insurance policy, commonly called Medigap. These are standardized plans sold by private insurers and labeled A through N. They pay the "gaps" the deductibles, coinsurance amounts, and copays that Original Medicare leaves behind. How Medicare Advantage Works Medicare Advantage plans officially Part C are offered by private insurers such as UnitedHealthcare, Humana, and Aetna. The federal government pays these insurers a fixed amount per enrollee per month, and the insurer delivers the Medicare benefit. The appeal is straightforward: many Medicare Advantage plans carry $0 monthly premiums, bundle Part D drug coverage, and include extras like dental, vision, hearing, and gym memberships. On paper, they look like a better deal than paying for Original Medicare plus a separate Medigap policy plus a Part D plan. The trade-offs emerge when you need care. ++ ++
Medicare Advantage plans use restricted provider networks Health Maintenance Organizations (HMOs) require referrals and limit care to in-network providers, while Preferred Provider Organizations (PPOs) allow out-of-network care at higher cost. The practical consequence is that not every doctor, hospital, or specialist who accepts Medicare accepts your specific Medicare Advantage plan. This was already a limitation. In 2026, it has become a more acute problem. Multiple major health systems have terminated their contracts with Medicare Advantage insurers, citing inadequate reimbursement rates and excessive administrative burden from prior authorization requirements. Kettering Health, for example, ended its contracts with Humana and Devoted Health after 2025. Nationally, an estimated one in ten Medicare Advantage members may be forced to switch plans as insurers exit certain geographic markets entirely. For someone managing a chronic condition who has built a relationship with specific physicians and specialists, a network disruption is not merely inconvenient it is a direct threat to continuity of care.
This is the most important structural risk of Medicare Advantage that most people never learn until it is too late. In most states, Medigap insurers are only required to accept applicants without medical underwriting during one specific window: the six months immediately following your initial enrollment in Medicare Part B at age 65. Outside of that window, insurers can review your health history and either deny your application or charge substantially higher premiums based on your health status. Here is how this creates a trap: if you enroll in a Medicare Advantage plan at 65 because the $0 premium looks attractive, stay in that plan for several years, and then develop a chronic condition cancer, heart disease, diabetes, kidney disease you may find yourself unable to switch back to Original Medicare with Medigap coverage when you need it most. You are effectively locked into the managed care structure. Limited exceptions exist. If your Medicare Advantage plan leaves the market or stops serving your area, or if you are in your first year of Medicare Advantage enrollment, you have Guaranteed Issue Rights the ability to switch to Original Medicare and obtain a Medigap policy without underwriting. Outside of these exceptions, the window is largely closed. Feature Original Medicare + Medicare Advantage** Medigap** Provider Access Any Medicare-accepting In-network providers provider nationwide only (HMO/PPO) Monthly Premium Part B ($202.90) + Often $0 to low Medigap (~$165/mo at monthly premium 65) Out-of-Pocket Maximum Very low (Medigap Varies by plan; covers most costs) required by law Prior Authorization Rarely required Commonly required for procedures Drug Coverage Requires separate Part Usually bundled D plan Switching Flexibility Can drop Medigap Hard to switch back to anytime (subject to Medigap with a chronic underwriting) condition Dental/Vision/Hearing Not included Often included as extras
Original Medicare plus a Medigap policy tends to work better for people who have established relationships with specific physicians, anticipate specialist care, travel frequently, or live part of the year in different regions of the country. The predictability of knowing that 90% of doctors are accessible, with minimal paperwork, has significant value as health complexity increases with age. Medicare Advantage tends to work better for people who are relatively healthy, comfortable with in-network care, and for whom the extras dental, vision, gym memberships represent genuine value they would use. The $0 premium is real money saved, as long as the network holds and care needs remain routine. The decision made at 65 can have consequences that are very difficult to undo at 75 or 80. That asymmetry is the central fact most people are not told before they choose. ++ ++ The marketing materials for Medicare Advantage plans lead with what they offer. They do not lead with what they restrict. Understanding both sides of that trade-off is what separates a reactive enrollment decision from a deliberate one. Choosing between Medicare Advantage and Original Medicare is one of the most consequential decisions in retirement planning. Subscribe to the Retirement Shield newsletter for ongoing coverage of Medicare changes, or speak with a Medicare-specialized insurance broker who can walk through the plan options in your specific ZIP code network access, costs, and coverage gaps vary significantly by geography.