How Medigap works
Medigap (also called Medicare Supplement Insurance) is a private insurance product that “layers over” Original Medicare. It pays for some of the cost-sharing that Medicare itself doesn’t pay — deductibles, coinsurance, and copayments under Medicare Part A and Part B. It is not a replacement for Medicare; it’s an add-on.
The cost-sharing problem Medigap solves
Original Medicare covers most of your medical care, but it leaves you with several cost-sharing exposures: the Part A inpatient deductible per benefit period (a few thousand dollars in 2026), the Part A daily coinsurance after a long hospital stay, the Part B annual deductible (a few hundred dollars), the 20% Part B coinsurance on most outpatient services with no annual cap, and a few other gaps. For someone with a serious illness or a long hospital stay, these can total tens of thousands of dollars per year.
Medigap pays for most or all of these gaps, depending on the plan letter. The federal Medigap plan-letter system standardizes which benefits each policy covers; see the federal benefits matrix.
What Medigap does NOT cover
- Prescription drugs (Part D is a separate program)
- Long-term care (custodial nursing-home or in-home care)
- Vision care, dental care, and hearing aids
- Private-duty nursing
- Any medical care not covered by Original Medicare in the first place
For prescription drug coverage, you enroll in a separate Part D plan. For Part D Low-Income Subsidy (Extra Help) eligibility, see medicare.gov — Get help paying for prescription drugs or contact your state SHIP counselor. For long-term-care planning, your state SHIP counselor can also help you understand Medicaid long-term care options.
Medigap vs Medicare Advantage
Medicare Advantage (Part C) is an alternative to Original Medicare offered by private insurers under contract with CMS. An MA plan typically replaces Parts A and B with a managed-care product that may also include Part D drug coverage and additional benefits (dental, vision, hearing). MA plans use networks of providers; Original Medicare has no network.
You cannot have both Medigap and a Medicare Advantage plan at the same time.A Medigap policy only pays for cost-sharing under Original Medicare; if you’re enrolled in MA, your Medigap policy doesn’t pay anything. The MA-vs-Medigap decision is one of the most consequential in Medicare; we don’t walk through it here, but Medicare.gov/plan-compare and your state SHIP counselor are the right resources for that comparison.
Original Medicare cost-sharing structure and Medigap layer
Last verified:Source:medicare.gov — Medigap basics