Medigap Explained: What Medicare Supplement Insurance Covers — and What It Doesn’t

By Rana — Editor, Elite Era Trends

Original Medicare pays a large share of hospital and medical bills, but it does not pay everything. After Medicare pays its share, you can still owe deductibles, coinsurance and copayments — and, unlike many private plans, Original Medicare has no yearly cap on what you pay out of pocket. That gap is exactly what Medigap is for.

Medigap, formally called Medicare Supplement Insurance, is private insurance that helps pay some of the costs Original Medicare leaves behind. It does not replace Medicare. It sits alongside it: Medicare pays first, and then the Medigap policy pays some or all of the remaining cost-sharing, depending on the plan letter you buy. If you are weighing Original Medicare against a Medicare Advantage plan, or you are turning 65 soon, this guide explains what Medigap covers, what it does not cover, how the standardized plans differ, and — just as important — when you can buy one without facing medical underwriting.

Contents

• What Medigap is, in plain language
• What Original Medicare leaves you to pay
• What Medigap covers — and what it does not
• The standardized plan letters, explained
• Plan G, Plan N and the plans closed to new enrollees
• Medigap vs. Medicare Advantage
• When you can buy Medigap: the one-time 6-month window
• The December 7 deadline is a different window
• What Medigap costs, and how to shop
• Frequently asked questions
• Sources

What Medigap is, in plain language

Think of Original Medicare as two parts working together. Part A covers hospital care, and Part B covers doctor visits, outpatient care and many other medical services. Together they pay most of the bill for covered services, but they leave you with a share: a deductible you must meet, then usually 20% coinsurance on Part B services, plus hospital coinsurance for longer stays and other cost-sharing.

A Medigap policy picks up some or all of that leftover share. You keep paying your Part B premium, plus a separate monthly premium to the insurer. Medicare pays first; the insurer then pays its share of the remaining approved costs. Any doctor or hospital that accepts Medicare will generally accept your Medigap policy, since it simply supplements Original Medicare.

There is one eligibility rule to get out of the way early. To buy a Medigap policy, you generally need to be enrolled in both Part A and Part B. Medicare.gov states this plainly in its guide to buying a Medigap policy: the best time to buy is when you are 65 or older and first get Part A and Part B.

What Original Medicare leaves you to pay

The reason Medigap exists becomes clearer once you see the size of the gaps. In 2026, the Part A hospital deductible is $1,736 per benefit period, and the Part B deductible is $283 for the year. After the Part B deductible, you generally owe 20% of the Medicare-approved amount for most Part B services — doctor visits, outpatient procedures, lab work and durable medical equipment, among others. A hospital stay also brings daily coinsurance amounts after the first 60 days, and skilled nursing facility care brings daily coinsurance after the first 20 days.

Two features surprise people: the Part A deductible is per benefit period, not once per year, and Original Medicare has no annual out-of-pocket maximum, so a long illness can leave a large bill even after Medicare pays. Medigap does not make care free, but it can turn unpredictable cost-sharing into a predictable premium plus smaller known costs.

One caution: do not assume a 2026 deductible applies in 2027. Medicare updates these figures yearly, and the 2027 Part B deductible had not been published as a final CMS figure at the time of writing — ask any sales pitch quoting one for its CMS source.

What Medigap covers — and what it does not

Every standardized plan covers Part A coinsurance and hospital costs for up to 365 extra days after Medicare benefits end. Beyond that, coverage depends on the letter: Part B coinsurance (most plans in full; K at 50%, L at 75%); the Part A deductible (B, C, D, F, G and N in full; K at 50%, L at 75%, M at 50%); skilled nursing coinsurance; Part B excess charges (only F and G); the first three pints of blood yearly; and, in some plans, limited foreign travel emergency care.

Medigap’s name is helpful for what it does not do: it fills gaps in Original Medicare, it does not add benefits Original Medicare never had. In particular, Medigap does not cover prescription drugs — no Medigap policy sold today includes drug coverage, so if you want drug coverage alongside Original Medicare and Medigap, you need a separate stand-alone Part D plan. Our guide to 2027 Part D costs explains the 2027 deductible and the $2,400 out-of-pocket cap that apply to Part D, which is a separate piece of your coverage.

Medigap also does not cover routine dental, vision or hearing care, long-term custodial care, or private-duty nursing, and it is not travel insurance. Finally, a Medigap policy cannot be used to pay the copays and deductibles of a Medicare Advantage plan. The two routes are alternatives, not add-ons to each other — a point that catches people out every fall.

The standardized plan letters, explained

One of the most consumer-friendly features of Medigap is standardization. In most states, Medigap plans are identified by letters — A, B, C, D, F, G, K, L, M and N — and the same letter means the same core benefits no matter which insurer sells it. Plan G from one company covers the same benefits as Plan G from another company in the same state. What differs between insurers is the premium, any discounts, customer service and, in some cases, extra perks that sit outside the standardized benefits.

Three exceptions: Massachusetts, Minnesota and Wisconsin standardize differently. Everywhere else, shop mainly on price and service once you have chosen a letter — the cheapest Plan G is not a cut-down Plan G, and a higher premium does not buy broader standardized coverage.

Plan G, Plan N and the plans closed to new enrollees

For most people becoming eligible for Medicare today, the realistic choice narrows to a handful of letters, and two dominate the conversation.

Plan G is the most comprehensive plan open to new enrollees. It covers nearly every Medicare-approved gap, including Part B excess charges, except the annual Part B deductible, which you pay yourself. Plan G costs more in premium than less comprehensive plans.

Plan N usually carries a lower premium than Plan G, and that trade is explicit: you accept copayments of up to $20 for some office visits and up to $50 for an emergency room visit that does not lead to admission, and Plan N does not cover Part B excess charges. For someone who rarely visits the doctor and is comfortable with small copays, that trade can save money over a year. For someone who sees specialists often or worries about excess charges, the copays and the excess-charge gap can erase the premium saving.

Plans C and F are the other end of the story. They are the only plans that cover the Part B deductible, and Plan F is the most comprehensive Medigap plan ever sold. But federal law closed them to people who became eligible for Medicare on or after January 1, 2020. If you became eligible before that date, you may still be able to buy or keep one; if you became eligible after it, they are not an option, and Plan G is the closest equivalent. Our next posts in this series will compare Plan G and Plan N in detail for 2027, and then explain the high-deductible version of Plan G. Plans K and L, meanwhile, cover only a percentage of many benefits, but they are the only Medigap plans with an annual out-of-pocket limit — a smaller-group option that deserves a careful look at the percentage math first.

Medigap vs. Medicare Advantage

It helps to state the fork in the road plainly. Original Medicare plus Medigap plus a Part D plan is one route: you pay a Part B premium, a Medigap premium and a Part D premium, and in return you generally get nationwide access to any provider that accepts Medicare, with Medigap smoothing the cost-sharing. Medicare Advantage is the other route: a single private plan replaces Original Medicare for your coverage, usually bundles drug coverage, often adds dental or vision extras, and manages care through a provider network with its own copays, prior authorization rules and an annual out-of-pocket maximum.

Neither route suits everyone: it depends on your doctors, drugs, travel, health and budget. A local Advantage network with bundled extras and a capped maximum can be the better deal; travelling, splitting time between states, or wanting any Medicare-accepting specialist without referrals can favour Original Medicare plus Medigap. Compare total yearly cost, not premiums alone, and run the doctor-and-drug check in our December 7 checklist guide before any switch — see also Medicare Advantage changes for 2027.

When you can buy Medigap: the one-time 6-month window

This is the section to read twice if you are approaching 65. Your Medigap Open Enrollment Period is a one-time, six-month window that begins on the first day of the month in which you are both 65 or older and enrolled in Part B. During that window, an insurer must sell you any Medigap policy it offers in your state, cannot deny you because of pre-existing health conditions, and cannot charge you more because of your health.

After that window closes, without a guaranteed-issue right, an insurer may use medical underwriting: ask health questions, deny you, charge more, or impose a pre-existing-condition waiting period, subject to state law. Some states add stronger protections, but federal law alone gives no yearly right to switch without underwriting.

Guaranteed-issue rights are the exception: they apply when, for example, an Advantage plan leaves your area, you move out of a plan’s service area, you lose employer or union supplemental coverage, or you exercise a trial right after first joining Advantage. Most windows last 63 days, and the plans available may be limited — see KFF’s overview of Medigap guaranteed-issue requirements. If you may ever want Medigap, decide in the six-month window, even if you feel healthy.

The December 7 deadline is a different window

Every fall, Medicare’s annual Open Enrollment Period runs from October 15 to December 7. In that window you can join, drop or switch a Medicare Advantage plan or a Part D drug plan, and changes take effect on January 1. Our 2027 open enrollment checklist walks through that window in detail.

December 7 does not reopen your Medigap window: that six-month window happens once and does not reset each fall. You can use the fall window to leave Advantage and return to Original Medicare, but that alone does not guarantee a Medigap policy. If you are considering that move, apply first and get the insurer’s decision in writing, and get free help from your State Health Insurance Assistance Program (SHIP) — its counselors do not sell plans.

If you already have Medigap, still use the fall window to review Part D, since drug formularies change yearly. If you receive extra help with costs, the Medicare ACCESS program guide explains a separate set of supports.

What Medigap costs, and how to shop

Premiums vary widely by letter, insurer, age, ZIP code and pricing method, so this guide quotes no national “typical” premium. Ask whether an insurer uses community rating, issue-age rating or attained-age rating, and how its premiums for your letter have moved in recent years — that history beats a single first-year quote.

Ask about household or non-smoker discounts, and remember the full monthly picture: Part B premium plus Medigap premium plus a Part D premium. Be wary of pitches that pressure a same-day decision, quote a 2027 deductible without a CMS source, or promise dental, vision, drug or long-term-care cover.

To shop, in order: confirm Part A and Part B and your window; choose a letter, then an insurer; check Medicare.gov for your state; get several quotes for the same letter; price Part D alongside it; get any switch in writing before dropping Advantage cover; and talk to SHIP if unclear.

Medigap is not glamorous coverage — no gym membership or dental card. What it does, chosen in the right window, is turn a major uncertainty into a known premium and a short list of remaining costs. Next in this series: Plan G vs Plan N, switching without underwriting, and high-deductible Plan G. If you are turning 65 soon, start with your six-month window: it does not come back.

Frequently asked questions

Sources

• Medicare.gov — Buying a Medigap policy
• Medicare.gov — Joining a health or drug plan
• KFF — Medigap guaranteed-issue requirements

General information only, not personal advice. Confirm your options at Medicare.gov, with 1-800-MEDICARE, or through SHIP before enrolling.