Medigap vs Medicare Advantage: what Medigap actually is and how it compares

Short answer

Medigap — also called Medicare Supplement — is private insurance that pays for costs Original Medicare doesn’t fully cover. It doesn’t replace Original Medicare; it works alongside it. Any provider that accepts Medicare accepts your Medigap. Ten plan letters (A through N) are federally standardized — a Plan G from any carrier covers the same things as a Plan G from any other carrier. The differences are premium and service quality.

What is Medigap?

Medigap is private health insurance sold by state-licensed carriers that pays the cost-sharing gaps in Original Medicare — deductibles, coinsurance, and hospital costs after Part A days are exhausted. It only works with Original Medicare, not with Medicare Advantage.

Ten plan letters are federally standardized: A, B, C, D, F, G, K, L, M, and N. The federal standardization means a Plan G from one carrier covers the same benefits as a Plan G from any other carrier. What differs between carriers on the same letter is the monthly premium, financial stability, and customer service. Plan F closed to newly eligible beneficiaries on January 1, 2020; new enrollees typically choose Plan G or Plan N.

Why Medigap exists — a short history

When Congress passed Medicare in 1965, the program covered hospital and medical benefits but left beneficiaries with meaningful cost-sharing: deductibles for hospital stays, coinsurance for doctor visits, and uncapped exposure on long hospitalizations. Older adults on fixed incomes needed a way to close those gaps.

Private “Medicare supplement” policies emerged in the 1970s and 1980s to fill those gaps, but they were unregulated and highly variable. Carriers sold overlapping policies, confusing plan structures, and misleading marketing was widespread. Some beneficiaries were sold multiple policies that duplicated coverage; others bought policies they didn’t understand.

In 1990, Congress passed the Omnibus Budget Reconciliation Act (OBRA), which federally standardized Medigap into 10 plan letters starting in 1992. From that year forward, consumers could compare policies apples-to-apples — a Plan G was a Plan G no matter who sold it. Later legislation refined the standards: MIPPA in 2008 and the ACA in 2010 added consumer protections. Plans F and C were closed to newly eligible beneficiaries on January 1, 2020 (people already enrolled kept them), because those plans covered the Part B deductible in a way that overlapped with cost-transparency reforms.

The standardization is why Medigap is easier to shop today than most private insurance — the product is fixed, and the shopping question is which carrier to buy it from.

How Medigap differs from Medicare Advantage — at the category level

Same starting point (Part A and Part B benefits). Fundamentally different structures. If you want the foundational comparison between the two categories at product-neutral level, see our Medicare Advantage vs Medicare guide.

Different structure

Medigap is a wrapper around Original Medicare — you keep Medicare fee-for-service and Medigap pays what Medicare doesn’t. Medicare Advantage replaces Original Medicare — the plan takes over both Medicare and (usually) drug coverage into one product. The same Part A and Part B benefits are covered on both paths, but delivered through fundamentally different systems: fee-for-service plus wrap versus private-plan replacement.

Different provider access

Medigap doesn’t have networks. Any provider that accepts Medicare — which is most physicians and hospitals nationwide — accepts your Medigap. Medicare Advantage has networks: HMO, PPO, and POS variants that restrict where you can be treated. For provider stability, Medigap wins on structure alone.

Different cost model

Medigap costs a monthly premium — typically $100 to $300 depending on plan letter, state, age, tobacco use, and (in most states) medical history. In exchange, most Medicare-approved services have near-zero out-of-pocket cost. Medicare Advantage typically has a low or zero monthly premium, but you pay copays and coinsurance during the year up to an annual out-of-pocket cap.

Different regulatory posture

Medigap is regulated by state insurance departments plus federal standardization on plan letters. Medicare Advantage is regulated by CMS as a federal contract with private carriers. State regulation gives Medigap consumer protections a state-by-state character — some states are more permissive on underwriting, others require year-round guaranteed-issue. Medicare Advantage is uniform at the federal level.

The 10 Medigap plan letters explained

All 10 letters cover the same benefits per letter across every carrier. Here is what each group covers.

The most popular current plans

• Plan G — the most common choice for newly eligible beneficiaries. Pays everything Original Medicare doesn’t except the Part B deductible for the first year.
• Plan N — a lower-premium alternative to Plan G. Similar coverage but with small copays for some doctor and emergency room visits, plus you pay excess charges if your provider does not accept Medicare assignment.

The legacy plans (closed to newly eligible)

• Plan F — closed to newly eligible after January 1, 2020. Covered the Part B deductible in addition to everything Plan G covers. People enrolled before that date kept their coverage.
• Plan C — closed to newly eligible after January 1, 2020. Similar to Plan F but with slightly different coverage details.

The high-deductible variants

• Plan G high-deductible variant — same coverage as Plan G but you meet an annual deductible before benefits pay. Lower monthly premium; higher upfront cost when you need care.
• Plan F high-deductible variant — same coverage as Plan F but with the deductible; closed to newly eligible with the standard Plan F.

The cost-sharing plans

• Plan K — pays 50% of most cost-sharing (coinsurance, copays) after a lower monthly premium.
• Plan L — pays 75% of most cost-sharing with a moderate monthly premium.

Other letters (A, B, D, M)

Plans A, B, D, and M each cover a specific subset of Medicare cost-sharing. Standardization means the coverage details are identical across carriers within each letter. These plans are less commonly sold today but remain available in most states.

When you can enroll in Medigap and why timing matters

Your Medigap Open Enrollment Period is a 6-month window that starts the month you turn 65 and are enrolled in Part B. During this window, Medigap is guaranteed-issue nationwide — no medical underwriting, no denials, no pre-existing condition exclusions. You can pick any letter from any carrier that sells in your state, and the carrier must accept you at their standard rate.

Outside this window, most states allow carriers to underwrite. Underwriting means the carrier can decline you based on health history, charge higher premiums for health conditions, or impose waiting periods on pre-existing conditions.

The 4 states with year-round guaranteed-issue

• Connecticut
• Massachusetts
• Maine
• New York

In these states, Medigap carriers must accept you at any time of year, regardless of health status.

The birthday-rule states

• California, Missouri, Oregon, and Washington offer time-bounded switching windows around your birthday. You cannot enroll new during those windows if you never had Medigap, but if you already have a policy you can switch to a comparable letter from a different carrier without underwriting.

The trial-right guarantee — 12-month Medicare Advantage re-entry

If you switched to Medicare Advantage as your first Medicare plan and change your mind within 12 months, federal trial-right protection guarantees Medigap acceptance nationwide when you switch back. This is a one-time safety net designed for people who tried Medicare Advantage and want to return to Original Medicare plus Medigap.

Why some seniors choose Medigap over Medicare Advantage

Medigap suits people who value provider stability (any Medicare-accepting doctor works), cost predictability (near-zero variable cost after the premium), and travel flexibility (works anywhere Medicare is accepted). It costs more per month than Medicare Advantage. For high-utilizers, multi-chronic-condition patients, and people who travel or split time between states, Medigap’s higher premium often costs less over 12 months than Medicare Advantage’s copay-and-cap exposure plus prior-authorization friction.

Why some seniors choose Medicare Advantage over Medigap

Medicare Advantage suits people who value lower monthly cost, want included extras like dental, vision, hearing, and transportation, are generally healthy and low-utilization, and are willing to work within a network and prior-authorization process. It gives up provider stability and cost predictability in exchange for structure and extras. For dual-eligibles and Special Needs Plan qualifiers, the D-SNP and C-SNP variants of Medicare Advantage often outperform Medigap because they coordinate with Medicaid or wrap around a chronic condition.

How Baba helps you understand this category

The Medigap vs Medicare Advantage question is bigger than “which is cheaper.” It is about which structure serves your life. A patient advocate walks you through your provider list, your travel pattern, your condition list, and your risk tolerance — then helps you match a category to your situation, not a product to a sales pitch.

Frequently asked questions

Is Medigap the same as Medicare Supplement?

Yes. “Medigap” and “Medicare Supplement” are two names for the same product. Federal regulations use both terms; carriers, brokers, and consumer publications use them interchangeably. The federal standardization applies to the same 10 plan letters (A through N) regardless of which name is used.

What are the 10 Medigap plan letters?

Plans A, B, C, D, F, G, K, L, M, and N. Coverage per letter is federally standardized — a Plan G from one carrier covers the same benefits as a Plan G from any other carrier. Plans F and C are closed to newly eligible beneficiaries after January 1, 2020. Plans G and N are the most commonly chosen by new enrollees.

Can I have both Medigap and Medicare Advantage?

No. Medigap only works with Original Medicare. If you enroll in Medicare Advantage, a Medigap carrier cannot legally sell you a new Medigap policy, and an existing Medigap policy will not pay for services covered under Medicare Advantage.

What happens if I miss my Medigap Open Enrollment Period?

Outside the 6-month window at age 65, most states allow Medigap carriers to underwrite. That means they can deny you, charge higher premiums, or impose waiting periods on pre-existing conditions. Four states — Connecticut, Massachusetts, Maine, and New York — offer year-round guaranteed-issue. Trial-right protection covers you if you enrolled in Medicare Advantage as your first Medicare plan and switch back within 12 months.

Why did Congress standardize Medigap?

The 1970s and 1980s saw widespread confusion and marketing abuses in private Medicare supplement policies — beneficiaries were sold overlapping policies with unclear benefits. In 1990, OBRA standardized Medigap into 10 federal plan letters (effective 1992) so consumers could compare policies apples-to-apples. Later legislation (MIPPA 2008, ACA 2010) added consumer protections; Plans F and C closed to newly eligible enrollees in 2020.

This information is for educational purposes and should not substitute for professional guidance. Healthcare coverage details vary by individual plan. Consult with Baba’s support team or your insurance provider for information specific to your situation.