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Medigap: the policy that caps the 20%, and the window that closes

Short answer: Medigap is private insurance that pays the gaps Original Medicare leaves, above all the Part B coinsurance of 20% that otherwise has no annual limit. Plans are standardized by letter, so every insurer’s Plan G covers exactly the same things, which makes the comparison purely about price and company behavior. The decision is really about timing: for six months after your Part B starts, insurers must sell you any policy at their standard rate regardless of health. After that, most states let them ask about your health and say no.

By the Medicare Decoder team · Updated October 12, 2026 · 4-minute read · Figures are official CMS amounts, checked against CMS

Key takeaways

Medigap works only with Original Medicare, never with a Medicare Advantage plan.
Benefits are standardized by letter; Plan G and Plan N are the two most people choose today.
Plan F and Plan C are closed to anyone who became eligible on or after January 1, 2020.
Your guaranteed-issue window is six months from when Part B starts, and it does not come back.
Prices for identical coverage vary two to three times over, driven mostly by the insurer’s pricing method.

Jump to Why people buy it The lettered plans What drives price The six-month window How to buy well FAQ

Why Medigap exists

Original Medicare pays 80% of Part B services after a $283 deductible in 2026. It does not cap the other 20%. For an ordinary year that is a manageable number; for a year involving cancer treatment, dialysis, or major surgery, 20% of a very large bill remains a very large bill. Medigap converts that open-ended exposure into a fixed monthly premium. It also covers the Part A hospital deductible of $1,736 per benefit period and adds 365 extra hospital days beyond what Medicare covers.

What Medigap does not do: cover prescriptions (that is Part D), cover dental, vision, or hearing, or work alongside an Advantage plan. It is the companion to Original Medicare, and only to Original Medicare.

The lettered plans

Plan	Covers Part B coinsurance	Part B deductible	Excess charges	Notes
G	Yes, in full	No (you pay $283)	Yes	The most comprehensive plan available to new enrollees
N	Yes, minus small copays	No	No	Up to $20 office and $50 ER copays; lower premium than G
High-deductible G	Yes, after a $2,950 deductible in 2026	No	Yes	Much lower premium; catastrophic-style protection
F	Yes, in full	Yes	Yes	Closed to anyone newly eligible on or after January 1, 2020
K, L, M	Partial (50%, 75%, or with a shared deductible)	Varies	No	Lower premiums, more cost sharing; less commonly sold

Benefits within a letter are identical by law across insurers; only price, service, and rate history differ. Massachusetts, Minnesota, and Wisconsin standardize their plans differently.

In practice the real choice for most new enrollees is G versus N, compared in detail in that article, with high-deductible G as a third option for people comfortable self-funding the first layer. If you are wondering what happened to the plan your neighbor has, see the Plan F article.

What drives price, since benefits are identical

The same Plan G can differ by a factor of two or three between insurers in one ZIP code. The biggest driver is pricing method. Attained-age policies rise every year as you age and are usually cheapest at 65 and most expensive at 85, exactly when switching becomes hardest. Issue-age policies are priced on your age at purchase and never rise because you aged. Community-rated policies charge everyone the same. All three still rise for inflation and claims. Ask which method applies before you buy, and ask for the insurer’s rate-increase history for that plan in your state. The full pricing explanation.

Other factors: your state and ZIP code, tobacco use, household discounts of 5% to 12% that many insurers offer and almost none mention unprompted, and whether excess charges matter where you live (eight states ban them entirely).

The six-month window

Your Medigap open enrollment period begins the month you are 65 or older and enrolled in Part B, and runs six months. During it, insurers must sell you any policy they offer at their standard rate, cannot refuse you for health reasons, and cannot impose waiting periods beyond limited pre-existing condition rules. After it closes, most states permit medical underwriting: health questions, and the right to decline you or charge more.

Limited exceptions exist. Guaranteed issue rights apply in specific situations, including your Advantage plan leaving your area, an insurer misleading you, or trial rights if you tried Advantage for the first time and want out within the first year. A handful of states run annual or birthday-month switching windows with no underwriting. Everywhere else, the window is the window. This asymmetry is the main reason switching from Advantage to Medigap later is harder than people expect, and why the supplement decision is really a timing decision.

How to buy well

Pick the letter first, since benefits are fixed. Most people land on G or N.
Compare every insurer selling that letter in your ZIP code. Medicare’s Medigap tool lists them, and your state insurance department publishes rate comparisons.
Ask the four questions: which pricing method, what have rate increases been over five years, what discounts apply, and how long has the company sold this plan in this state.
Buy inside your window. A good policy you can get today beats a cheaper one you may not qualify for in five years.
Add a Part D plan separately, because Medigap does not cover drugs, and skipping Part D triggers a permanent penalty (even if you take nothing).
Get free help if you want it. SHIP counselors walk through state rate comparisons with no commission at stake.

Questions people also ask

What is Medigap and what does it cover?

Medigap is private supplemental insurance that pays costs Original Medicare leaves behind, above all the 20% Part B coinsurance that has no annual limit, plus the Part A hospital deductible and 365 extra hospital days. It does not cover prescriptions, dental, vision, or hearing, and cannot be used with a Medicare Advantage plan.

Which Medigap plan is best?

For most new enrollees the choice is Plan G, which covers everything except the Part B deductible, or Plan N, which costs less in exchange for small office and emergency room copays. High-deductible Plan G offers a much lower premium with a $2,950 deductible in 2026.

Why is Plan F no longer available?

Plan F and Plan C are closed to anyone who became eligible for Medicare on or after January 1, 2020, because federal law barred new plans from covering the Part B deductible. People already enrolled can keep them.

When can I buy a Medigap policy without health questions?

During your six-month Medigap open enrollment period, which starts when you are 65 or older and enrolled in Part B. In that window insurers must sell you any policy at their standard rate regardless of health. After it, most states allow medical underwriting.

Why do Medigap prices vary so much for the same plan?

Because benefits are standardized but premiums are not. Insurers use different pricing methods (attained-age, issue-age, or community-rated), price by geography, and set their own rate increases, so identical coverage can cost two or three times more from one company than another.

Sources for this article

Medicare.govBuying a Medigap policy: standardized plans, pricing methods, and what each letter covers.
Medicare.govWhen to buy Medigap: the open enrollment window and guaranteed issue rights.
CMS.gov2026 premiums and deductibles: the deductibles and coinsurance Medigap covers.

Figures checked against these sources on October 12, 2026. We update within days when CMS publishes new amounts.

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