Medigap (Medicare Supplement Insurance) is private health insurance that helps pay certain out-of-pocket costs that remain after Original Medicare (Part A and Part B) pays its share. Standardized Medigap policies cover specified combinations of deductibles, copayments, and coinsurance, depending on the policy’s plan type and the enrollee’s eligibility.

Plain-Language Summary: Medigap is supplemental insurance that can cover some of the “gaps” in Original Medicare’s cost sharing. It does not replace Medicare, and it does not cover all health-related expenses.

Context

Original Medicare generally involves cost sharing, including deductibles, coinsurance, and copayments. Medigap developed as a standardized form of supplemental coverage intended to reduce variation in what beneficiaries pay out of pocket for Medicare-covered services.

In most states, Medigap benefits are organized into lettered plan types (commonly Plans A through N). Under standardization rules, a plan letter corresponds to a defined set of benefits, meaning a given lettered plan is designed to cover the same benefits regardless of the insurer offering it, though premiums and administrative features may differ. State rules can modify how policies are offered, and some states provide additional consumer protections beyond federal minimums.

Medigap is generally used alongside Original Medicare rather than with Medicare Advantage (Part C). In operational terms, Medigap typically functions as secondary coverage: Medicare pays first for covered services, and the Medigap policy may pay some or all of the remaining approved cost sharing, depending on the plan design. Medicare Advantage is a different delivery pathway for Medicare benefits, usually with its own cost-sharing rules and network arrangements.

Access to Medigap can be influenced by enrollment timing and underwriting rules. A commonly referenced period is the Medigap Open Enrollment Period, which is generally tied to being age 65 or older and enrolled in Medicare Part B. During this period, federal rules commonly limit health-based underwriting for certain purchases. Outside protected periods, and depending on state law and individual circumstances, insurers may apply medical underwriting, which can affect eligibility and premiums.

Medigap policies generally do not include outpatient prescription drug coverage. Prescription drug coverage is typically provided through Medicare Part D or other forms of creditable prescription coverage.

Misunderstandings

Medigap is sometimes described as a substitute for Medicare. It is not primary coverage and generally pays only after Original Medicare has processed a claim.

Another common misunderstanding is that all Medigap policies are identical in all respects. While benefits are standardized by plan letter in most states, premiums, underwriting practices, customer service, and certain administrative features can vary by insurer, and state-specific rules can affect availability.

Medigap is also sometimes assumed to cover long-term custodial care, routine dental, vision, or hearing services, or unlimited foreign travel health costs. Medigap benefits are limited to what is defined for the plan type and do not imply broader coverage.

Medigap is sometimes conflated with Medicare Advantage because both can involve private insurers. Medigap supplements Original Medicare, while Medicare Advantage is an alternative way to receive Medicare benefits.