Medicare Supplement (Medigap) Plans Explained: Coverage, Costs, and How to Enroll

If you are enrolled in Original Medicare, you already know it does not cover everything. Part A and Part B leave you responsible for deductibles, coinsurance, copayments, and — most critically — there is no annual cap on what you might owe out of pocket. A single major hospitalization or surgery could cost you tens of thousands of dollars.

That is where Medicare Supplement insurance comes in. Commonly known as Medigap, these policies are specifically designed to fill the financial gaps that Original Medicare leaves behind. This guide covers what Medigap plans cover, how the 10 standardized plans compare, what they cost, and how to enroll at the right time.

What Is a Medigap (Medicare Supplement) Plan?

A Medigap policy is a private health insurance plan that supplements your Original Medicare coverage. It is sold by private insurance companies licensed in your state, but the benefits are standardized by the federal government. When you have a Medigap plan, Original Medicare pays its share of covered costs first, and then your Medigap policy kicks in to pay some or all of the remaining costs — depending on which plan you choose.

There are a few important things to understand upfront:

• Medigap only works with Original Medicare (Part A and Part B). If you have a Medicare Advantage plan, you cannot use a Medigap policy.
• Medigap policies cover only one person. If both you and your spouse want coverage, you each need your own policy.
• Medigap does not include prescription drug coverage. You need a separate Medicare Part D plan for medications.
• The policy is guaranteed renewable. As long as you pay your premiums, the insurance company cannot cancel your Medigap policy regardless of your health.

How Medigap Works With Original Medicare

When you visit a doctor or hospital, you present both your Medicare card and your Medigap insurance card. The provider bills Medicare first. Medicare pays its portion under Part A or Part B. Then the remaining balance — your deductible, coinsurance, or copayment — gets sent to your Medigap insurer, which pays according to your plan’s benefits.

For example, say you have an outpatient procedure that costs $10,000. Under Original Medicare alone, you would pay the Part B deductible plus 20% coinsurance — roughly $2,205 out of pocket. With Medigap Plan G, the plan pays the entire 20% coinsurance. You only owe the annual Part B deductible ($257 in 2025). Because Medigap works with Original Medicare, you retain full access to any doctor or hospital that accepts Medicare nationwide. There are no networks, no referral requirements, and no prior authorization.

The 10 Standardized Medigap Plans

Federal law standardizes Medigap into 10 letter-designated plans: A, B, C, D, F, G, K, L, M, and N. Each plan letter offers a specific set of benefits. A Plan G from one company covers the exact same benefits as a Plan G from any other company — only the premium, customer service, and financial rating differ.

Plan A — Basic Benefits Only

The most basic plan. Covers Part A coinsurance and hospital costs for up to 365 additional days after Medicare benefits are used up, Part B coinsurance or copayment, and the first three pints of blood. Does not cover the Part A or Part B deductible, skilled nursing facility coinsurance, or foreign travel emergencies.

Plan B — Basic Benefits Plus Part A Deductible

Includes everything in Plan A and adds coverage for the Part A hospital deductible ($1,676 per benefit period in 2025). Still does not cover the Part B deductible, skilled nursing facility coinsurance, or foreign travel emergencies.

Plan C — Comprehensive (Closed to New Enrollees After 2020)

Covers the Part A deductible, Part B deductible, skilled nursing facility coinsurance, and foreign travel emergencies on top of all basic benefits. Because it covers the Part B deductible, Plan C is no longer available to anyone newly eligible for Medicare on or after January 1, 2020.

Plan D — Similar to G Without Excess Charges Coverage

Covers the Part A deductible, skilled nursing facility coinsurance, and foreign travel emergencies, along with all basic benefits. The only difference from Plan G is that Plan D does not cover Part B excess charges.

Plan F — The Former Gold Standard (Closed to New Enrollees After 2020)

Plan F was the most popular Medigap plan for decades because it covers everything — all deductibles, all coinsurance, skilled nursing facility costs, Part B excess charges, and foreign travel emergencies. Like Plan C, it is closed to people newly eligible for Medicare on or after January 1, 2020 because it covers the Part B deductible. Existing policyholders are grandfathered in.

Plan G — The New Gold Standard

The most popular plan for new enrollees. Covers everything Plan F covers except the annual Part B deductible — meaning you pay $257 once per year (2025 amount) and your plan covers everything else. A high-deductible version of Plan G is also available with lower monthly premiums but a $2,870 deductible (2025) before the plan begins paying.

Plan K — 50% Cost-Sharing With an Out-of-Pocket Limit

Instead of covering 100% of cost-sharing, Plan K covers 50%. You split the Part A deductible, coinsurance, skilled nursing facility costs, and blood charges with the plan. The key feature is an annual out-of-pocket limit ($7,060 in 2025) — once you reach it, the plan pays 100% for the rest of the year.

Plan L — 75% Cost-Sharing With a Lower Limit

Works like Plan K but pays 75% of cost-sharing with a lower annual out-of-pocket limit ($3,530 in 2025). Offers a middle ground between full-coverage plans and Plan K.

Plan M — Partial Part A Deductible Coverage

Covers 50% of the Part A deductible plus basic benefits, skilled nursing facility coinsurance, and foreign travel emergencies. Does not cover the Part B deductible or Part B excess charges. Less commonly available.

Plan N — Lower Premiums With Small Copays

The second most popular plan. Covers the Part A deductible, skilled nursing facility coinsurance, foreign travel emergencies, and basic benefits. Requires a copay of up to $20 for some office visits and up to $50 for emergency room visits that do not result in admission. Does not cover Part B excess charges. Premiums are typically 15% to 30% lower than Plan G.

Most Popular Plans: Plan G and Plan N

Since Plan F was closed to new beneficiaries after 2020, the market has consolidated around Plan G and Plan N. Together, these two plans account for the majority of new Medigap enrollments.

Plan G is the go-to choice for people who want near-complete coverage and predictable costs. After you pay the annual Part B deductible, your out-of-pocket exposure for Medicare-covered services is essentially zero. Plan G is especially popular among beneficiaries with chronic conditions or those who see multiple specialists.

Plan N appeals to people who are healthy, visit the doctor less frequently, and want a lower monthly premium. The trade-off is small copays at some visits and no coverage for Part B excess charges — though excess charges are increasingly rare since most doctors accept Medicare assignment. Plan N can save you $400 to $700 or more per year compared to Plan G.

What Medigap Covers (and What It Does Not)

Medigap can only help pay for services that Original Medicare already covers. It fills the cost-sharing gaps — it does not expand what Medicare covers.

What Medigap typically covers:

• Part A coinsurance and hospital costs (up to 365 additional days after Medicare benefits are exhausted)
• Part B coinsurance or copayment (the 20% you normally owe for outpatient services)
• Part A hospital deductible ($1,676 per benefit period in 2025)
• Skilled nursing facility coinsurance (days 21-100)
• First three pints of blood
• Part B excess charges (Plans F and G only)
• Foreign travel emergency care (most plans except A, B, and K)

What Medigap does not cover:

• Prescription drugs (you need a separate Part D plan)
• Routine dental, vision, or hearing care
• Long-term care or custodial care
• Private-duty nursing
• Any service that Medicare itself does not cover

Medigap vs. Medicare Advantage: When to Choose One Over the Other

This is one of the most important decisions you will make when setting up your Medicare coverage. Medigap and Medicare Advantage are fundamentally different products that cannot be used together.

Choose Medigap (with Original Medicare) if:

• You want unrestricted access to any Medicare-accepting doctor or hospital nationwide
• You travel frequently or split time between states
• You have chronic health conditions and want to avoid prior authorization hurdles
• You prefer predictable, low out-of-pocket costs and can afford a higher monthly premium

Choose Medicare Advantage if:

• You want the lowest possible monthly premium
• You want dental, vision, hearing, and drug coverage in a single plan
• Your preferred doctors are in the plan's network and you primarily use local providers
• You are generally healthy and do not anticipate needing frequent specialty care

Important: If you choose Medicare Advantage and later want to switch to Original Medicare with a Medigap plan, you may face medical underwriting. In most states, insurers can reject your application or charge more if you have developed health conditions. There is a 12-month trial right if you are trying Medicare Advantage for the first time, but after that window closes, switching back becomes much harder. This is a critical consideration when making your initial choice at 65.

How to Enroll in a Medigap Plan

Timing is everything with Medigap enrollment. The best — and sometimes only — time to get a Medigap policy without health screening is during your Medigap Open Enrollment Period.

Medigap Open Enrollment Period

Your Medigap Open Enrollment Period is a one-time, six-month window that begins on the first day of the month when you are both age 65 or older and enrolled in Medicare Part B. During this period, insurance companies cannot deny you coverage, cannot charge you more because of health problems, and must cover pre-existing conditions (though a waiting period of up to six months may apply for conditions treated or diagnosed recently).

This window does not come back. Once the six months are over, you lose these guaranteed protections in most states. Virtually every Medicare advisor recommends applying for Medigap during this window, even if you are in perfect health today.

Guaranteed Issue Rights

Outside of the Open Enrollment Period, there are specific situations where federal law gives you guaranteed issue rights — meaning an insurer must sell you a Medigap policy without medical underwriting:

• Your Medicare Advantage plan leaves Medicare or stops covering your area
• You leave a Medicare Advantage plan within the first 12 months to return to Original Medicare (trial right)
• Your Medigap insurer goes bankrupt or your policy is not renewed through no fault of your own
• You dropped a Medigap policy to join Medicare Advantage for the first time and want to switch back within 12 months
• You left Medigap to join an employer group health plan and that coverage ends

How to Apply

You can apply for a Medigap plan by contacting insurance companies directly, working with an independent licensed insurance agent who can compare plans from multiple insurers, using your state’s free SHIP (State Health Insurance Assistance Program) for unbiased counseling, or using the Medicare Plan Finder tool at Medicare.gov to compare policies in your area.

How Much Does Medigap Cost?

Medigap premiums vary based on plan type, location, age, gender, and insurer. Here are general ranges for a 65-year-old:

• Plan G: $120 to $250 per month, with a national average of roughly $145 to $170
• Plan N: $90 to $190 per month, usually 15% to 30% less than Plan G from the same insurer
• Plan F (grandfathered): $180 to $350+ per month, often higher than Plan G because the remaining pool is older
• High-Deductible Plan G: $40 to $80 per month, but you must meet a $2,870 deductible (2025) before benefits begin

Three Pricing Methods to Understand

How a company prices its Medigap policies affects what you pay over time:

1. Community-rated: Everyone pays the same premium regardless of age. Premiums may increase due to inflation but not because you get older. Best for long-term cost stability.
2. Issue-age-rated: Premium is based on your age when you first buy the policy. It does not increase because of aging, but can go up for other reasons. The younger you buy, the lower your base rate.
3. Attained-age-rated: Starts low but increases as you age. Most common method, but can become expensive in your 70s and 80s.

Total Monthly Cost of Original Medicare With Medigap

For a complete picture, here is the total monthly cost for someone at age 65 with Original Medicare, Medigap Plan G, and a standalone Part D drug plan:

• Part B premium: approximately $185 per month (2025 standard amount)
• Medigap Plan G premium: approximately $145 to $170 per month
• Part D drug plan premium: approximately $30 to $50 per month
• Estimated total: $360 to $405 per month

This is higher than the typical Medicare Advantage monthly cost, where many enrollees pay only the Part B premium. But with Medigap, your annual out-of-pocket exposure for covered services is limited to the Part B deductible — roughly $257 — versus potentially thousands in copays and coinsurance before hitting a Medicare Advantage plan’s out-of-pocket maximum.

The Bottom Line

A Medigap policy is one of the most valuable tools available to Medicare beneficiaries who want financial predictability and unrestricted access to healthcare providers. It turns Original Medicare — which has no out-of-pocket limit and leaves you exposed to 20% coinsurance on every service — into a comprehensive coverage package where your costs are minimal and predictable.

The most important thing to remember is timing. Your Medigap Open Enrollment Period is a one-time, six-month window that gives you guaranteed access to any plan at standard rates regardless of your health. If you are approaching 65, start researching your options at least three months before your birthday. Compare plans from multiple insurers, understand how each company prices their policies, and make your decision before the window closes.

For most new enrollees, the decision comes down to Plan G or Plan N. Plan G offers near-complete coverage at a higher premium. Plan N saves money monthly but requires small copays. Either way, pairing Original Medicare with a Medigap policy gives you the freedom to see any Medicare-accepting provider in the country, with confidence that your out-of-pocket costs will be manageable.