Medicare Advantage (Part C) vs. Medigap (Medicare Supplement Insurance)

These two things are routinely presented as rivals on the same shelf, but they are not the same kind of object. Medicare Advantage is a delivery system: you still have Medicare, but a private plan administers your Part A and Part B benefits, usually through a network, usually with drug coverage folded in, and often with extra benefits attached. Medigap is an accessory to a different delivery system: you stay in Original Medicare, which pays first, and the Medigap policy pays some or most of what Original Medicare leaves on the table — deductibles, coinsurance, copays. So the real comparison is between two complete builds: Medicare Advantage as one bundle, versus Original Medicare plus a Medigap policy plus a stand-alone Part D drug plan. Once you see it that way, the trade-offs stop being mysterious.

The everyday difference is access and process. Under Original Medicare with Medigap, you can see any doctor or hospital in the U.S. that accepts Medicare, in most cases without referrals and without asking anyone's permission first. Under Medicare Advantage, non-emergency care generally happens inside the plan's network and service area, specialists may require referrals, and certain services may require prior authorization before the plan covers them. That last layer is not hypothetical: KFF's analysis of federal data found nearly 53 million prior authorization requests submitted to Medicare Advantage insurers in 2024, compared with just over 625,000 prior authorization reviews in traditional Medicare, which requires it only for a limited set of services. Most requests are approved, and among the small share of denials that get appealed, more than eight in ten are overturned — but the structure means approval processes are part of how the Advantage model manages care.

The money works in opposite directions. Medicare Advantage typically charges a low or even $0 plan premium and then collects copays and coinsurance as you use care, with an annual out-of-pocket maximum on covered services — a genuine ceiling that Original Medicare by itself does not have. The Medigap build inverts that: you pay a real premium every month (for the Medigap policy and for a Part D plan, on top of Part B), and in exchange your costs when you actually use care are small and predictable — how small depends on which standardized plan letter you buy. In a healthy year, the Advantage structure usually costs less in total; in a heavy-use year, the Medigap structure usually does. Neither is 'cheaper' as a category — they distribute the same risk differently.

Now the variable that most comparisons bury: the two paths are not equally reversible. Under federal law you get one 6-month Medigap Open Enrollment Period, starting the first month you have Part B and are 65 or older. During that window, an insurer cannot refuse to sell you any Medigap policy it offers, cannot medically underwrite you, and cannot price you up for pre-existing conditions. That window does not repeat. Outside it, unless you qualify for a federal guaranteed-issue right — a short list of situations, including a 12-month 'trial right' for people who joined a Medicare Advantage plan when first eligible and change their minds within the first year — insurers in most states can review your health history and deny you a Medigap policy or charge you more. A handful of states go further than federal law and guarantee ongoing or annual access to Medigap regardless of health; whether you live in one changes this calculus materially, and your State Health Insurance Assistance Program (SHIP) or state insurance department can tell you which rules apply where you live. The practical consequence: moving from Medigap to Medicare Advantage is an open door every year, while moving from Medicare Advantage to Medigap may be a door that has quietly locked behind you.

The extra benefits deserve a sober reading in both directions. Medicare Advantage plans may include routine dental, vision, and hearing benefits that Original Medicare doesn't cover — genuinely useful, but usually structured as capped allowances with plan-specific networks and rules, not open-ended insurance. Medigap adds none of those categories at all: it only pays cost-sharing on services Medicare already covers, so a Medigap household still self-funds routine dental and vision or buys separate coverage. Drug coverage splits the same way — usually included in an Advantage plan, never included in Medigap, always a separate Part D purchase on the Original Medicare path.

Because plans, networks, premiums, and extras vary by county and change every year, the way to ground this decision in your own numbers is the official plan finder at medicare.gov, a call to 1-800-MEDICARE, or free one-on-one counseling from your State Health Insurance Assistance Program (SHIP) — SHIP counselors are not paid to sell anything and can walk through both structures against your actual doctors, drugs, and budget.