What Is Medicare Supplement Insurance?

Medicare Supplement Insurance, commonly known as Medigap, is a type of private health insurance designed to help cover the out-of-pocket costs not paid by Original Medicare. These costs can include deductibles, copayments, and coinsurance. Medigap policies are standardized and regulated by federal and state laws to ensure consistent coverage options across insurers, although premiums and underwriting rules may vary.

Purpose and Function

Original Medicare, which includes Part A (hospital insurance) and Part B (medical insurance), covers many healthcare services but does not pay for everything. Beneficiaries often face cost-sharing responsibilities, such as the Part A deductible, Part B coinsurance, or charges for extended hospital stays. Medigap helps manage these expenses by covering some or all of these gaps, depending on the plan selected.

It’s important to note that Medigap only works with Original Medicare. It cannot be used in combination with Medicare Advantage (Part C) plans. Beneficiaries must be enrolled in both Medicare Part A and Part B to buy a Medigap policy.

Standardized Plan Options

Medigap plans are standardized into lettered options (Plans A through N), with each plan offering a specific set of benefits. For example, Plan G covers nearly all gaps in Original Medicare except the Part B deductible, while Plan N requires some copayments but offers lower premiums. Although the benefits of each plan type are standardized, premiums can vary based on the insurer, the beneficiary’s age, geographic location, and underwriting practices.

Some plans, such as Plans C and F, are no longer available to new Medicare enrollees as of January 1, 2020, although individuals who were eligible for Medicare before that date may still purchase them if offered.

Eligibility and Enrollment

The best time to purchase a Medigap policy is during the six-month Medigap Open Enrollment Period. This window begins the month a person turns 65 and is enrolled in Medicare Part B. During this time, insurance companies cannot deny coverage, impose waiting periods, or charge higher premiums due to health conditions.

Outside of this window, insurers may use medical underwriting to determine eligibility and pricing. This could result in denied applications or higher premiums, particularly for those with preexisting conditions. However, some states have additional protections or extended enrollment periods beyond the federal standard.

Medigap policies are individual contracts. If a married couple wants coverage, each person must buy a separate policy. Additionally, not all insurers offer all standardized plans in every state.

Coverage and Limitations

While Medigap helps pay for many costs not covered by Original Medicare, it does not cover everything. Most notably, Medigap policies do not include:

• Prescription drug coverage (Part D must be purchased separately)
• Long-term care services
• Vision and dental care
• Hearing aids
• Private-duty nursing

Because Medigap is secondary to Medicare, it only pays after Medicare has paid its share. If Medicare does not cover a service at all, Medigap will not provide coverage either.

Some Medigap plans offer coverage for foreign travel emergency care, but this is typically limited in scope and comes with a lifetime cap. Beneficiaries who travel internationally may need to consider additional travel insurance options.

Premiums and Cost Considerations

Premiums for Medigap policies are paid in addition to the monthly premium for Medicare Part B. Pricing can be structured in several ways:

• Community-rated: Everyone pays the same premium regardless of age.
• Issue-age-rated: Premiums are based on the age at the time of purchase and do not increase due to age.
• Attained-age-rated: Premiums increase as the policyholder ages.

In addition to premiums, policyholders may still be responsible for services not covered by either Medicare or the Medigap plan. Comparing the total potential costs—including premiums, out-of-pocket expenses, and risk exposure—can help beneficiaries choose the most cost-effective option for their situation.

Switching and Portability

Changing Medigap policies can be difficult after the initial enrollment period. In most states, insurers are not required to offer guaranteed issue rights beyond specific circumstances, such as losing other health coverage or moving out of a plan’s service area. These situations are known as “guaranteed issue rights” and allow a beneficiary to purchase certain Medigap plans without medical underwriting.

Some states allow broader rights to switch plans or have continuous open enrollment periods. Because regulations vary by location, individuals should check their state’s rules before attempting to change Medigap coverage.

Relationship to Other Coverage Types

Medigap differs from Medicare Advantage (Part C) in both structure and purpose. Medicare Advantage plans replace Original Medicare with coverage provided by private insurers, often including additional benefits like dental or vision. In contrast, Medigap supplements Original Medicare without altering the core benefits or provider access.

Medigap cannot be used with Medicare Advantage, and individuals must choose one path or the other. It is illegal for an insurer to sell a Medigap policy to someone enrolled in a Medicare Advantage plan, except during a valid switching period or trial right.

The Bottom Line

Medicare Supplement Insurance (Medigap) plays a critical role in helping Medicare beneficiaries manage healthcare costs that would otherwise be their responsibility under Original Medicare. While it does not add new benefits or replace Medicare coverage, it provides financial protection by covering deductibles, coinsurance, and copayments. Because of its standardized structure and enrollment rules, timing and comparison shopping are essential when considering a Medigap policy. Understanding its limitations, particularly regarding prescription drugs and extra services, is also key when evaluating overall healthcare needs.