How Medigap Supplemental Insurance Works: Plans G, N, and F Compared

Medicare Leaves Gaps That Can Cost Thousands. Medigap Covers Them.

Traditional Medicare (Parts A and B) covers approximately 80% of approved medical costs. The remaining 20% — copayments, coinsurance, and deductibles — falls to the beneficiary with no annual out-of-pocket maximum under Original Medicare. For a beneficiary hospitalized for 60 days and then undergoing surgery, those gaps can total $10,000 or more in a single year. Medigap, also called Medicare Supplement insurance, is private insurance sold specifically to fill those gaps. Approximately 13.4 million Medicare beneficiaries carry Medigap coverage, according to AHIP 2023 data.

What Medigap Actually Covers

Medigap policies are standardized by the Centers for Medicare and Medicaid Services (CMS). Federal law requires that any policy sold in most states with the same letter designation offer identical benefits, regardless of which private insurer sells it. This standardization allows comparison shopping by premium alone — the benefits are legally identical.

The Three Most Popular Plans

Plan G is the most comprehensive plan available to new Medicare enrollees (those who became eligible after January 1, 2020). It covers everything except the annual Part B deductible ($240 in 2024). Once the deductible is met, Plan G participants pay nothing for Medicare-covered services. Plan G has become the most popular Medigap plan, accounting for over 40% of all Medigap policies in force.

Plan N offers near-comprehensive coverage at a lower premium than Plan G, with two trade-offs: the beneficiary pays up to $20 for office visits and up to $50 for emergency room visits (waived if admitted). Plan N also does not cover Part B excess charges — the amount certain non-participating Medicare providers can charge above Medicare's approved rate (capped at 15%). Plan N typically costs 20%–35% less than Plan G annually, making it attractive for people who rarely use specialist care.

Plan F was the most comprehensive Medigap plan ever created, covering even the Part B deductible. However, Congress prohibited Plan F sales to new Medicare beneficiaries who became eligible on or after January 1, 2020. Existing Plan F holders can keep their coverage indefinitely, but the closed enrollment pool is aging, causing Plan F premiums to rise faster than other plans.

The Medigap Open Enrollment Window

The most important rule in Medigap is the open enrollment window. During a 6-month period that begins the month a beneficiary is both age 65 or older AND enrolled in Part B, insurers must sell any Medigap policy to that person at standard rates with no medical underwriting. The insurer cannot deny coverage or charge higher premiums based on pre-existing conditions during this window.

After the window closes, insurers in most states can use medical underwriting for new applicants. A person with diabetes, heart disease, cancer history, or other chronic conditions may be declined or quoted significantly higher premiums. Several states — including Connecticut, Maine, Massachusetts, New York, and Washington — have continuous guaranteed issue rules that provide ongoing protections.

Premium Variation by State and Age

Premiums are priced using one of three methods: community rating (same rate for all enrollees regardless of age), issue-age rating (based on age when policy purchased, never increases due to aging), or attained-age rating (increases as the beneficiary ages). Attained-age plans often appear cheapest at 65 but become the most expensive by age 80. Understanding pricing methodology before purchasing matters as much as the initial premium.

What Medigap Does Not Cover

• Prescription drugs — Part D coverage requires a separate standalone plan
• Dental, vision, and hearing care — not covered by Medicare at all; separate plans required
• Long-term custodial care (nursing home, home health aides for daily living activities)
• Services not covered by Medicare Parts A and B

Medigap cannot be used with Medicare Advantage (Part C) plans. Beneficiaries must choose between Original Medicare plus Medigap, or Medicare Advantage as a standalone alternative.

This article is for informational purposes only. Medicare rules, premiums, and deductibles change annually. Consult a licensed insurance agent or State Health Insurance Assistance Program (SHIP) counselor for personalized guidance.