Demystifying Medigap: How Medicare Supplement Plans Work

Original Medicare is good insurance with a hole in it. Part B generally pays 80% of approved outpatient charges and leaves the other 20% on you, with no annual maximum. A serious year of imaging, infusions, or post-surgical follow-ups can turn that uncapped coinsurance into a bill that dwarfs years of supplement premiums.

Medigap (Medicare Supplement Insurance) is the private policy built to sit behind Original Medicare and pay those standardized gaps. Official plan letters and benefits are on Medicare.gov's Medigap page. I spend a lot of enrollment season explaining that Medigap is not a replacement for Medicare. It is the secondary layer that makes Original Medicare predictable.

What the standardized letters actually cover

Federal law defines ten Medigap plan letters (A through N, with some letters retired for new enrollees). Each letter covers a fixed set of Medicare cost-sharing categories. Plan G and Plan N are what most new buyers consider today because Plan F and Plan C closed to newly eligible beneficiaries after 2019. Also, Plan G covers everything Plan F used to cover except the Part B deductible. Plan N covers the same major categories as Plan G but adds visit copays and excludes Part B excess charges. Plan A is the bare minimum. Plans K and L use percentage cost sharing with out-of-pocket caps.

The point is not memorizing every letter. The point is understanding that once you pick a letter, the benefits are identical regardless of carrier. A Humana Plan G and a Mutual of Omaha Plan G pay the same standardized shares. Only the premium, customer service, and rate trajectory differ.

Medigap and Medicare Advantage are mutually exclusive

You cannot hold a Medigap policy and a Medicare Advantage plan at the same time. It is one path or the other. Advantage replaces Original Medicare for most delivery purposes. Medigap supplements Original Medicare.

I see people try to keep both, or buy a supplement while still on an Advantage plan, thinking they are doubling up on protection. It does not work that way. If you want Medigap, you need to be on Original Medicare with Part A and Part B active, and you need to disenroll from any Advantage plan before the supplement can pay.

Switching from Advantage back to Original Medicare plus Medigap after your six-month open enrollment window usually triggers medical underwriting. That is the main reason to decide your path during Initial Enrollment, not three years later when a network problem surfaces.

How does a Medigap claim actually get paid?

Medicare pays first. Your supplement picks up the standardized remainder through an electronic crossover, and you rarely file a separate claim.

When you see a provider who accepts Medicare assignment, the office submits the claim to Medicare. Medicare processes it, pays its share, and forwards the remaining balance to your Medigap carrier automatically. Most of the time you never touch a form. You get a Medicare Summary Notice and a supplement explanation of benefits showing what each layer paid.

You owe a balance only when Medicare denied the service, when you have not met the Part B deductible yet, or when your plan letter excludes that cost category (Plan N copays, for example). Keep your MSN and supplement EOB for at least six months. Billing offices occasionally miscode a claim, and those documents are what you need to get it corrected.

If a provider opts out of Medicare entirely, neither Medicare nor Medigap pays. That is why verifying provider participation before you buy matters more than comparing premium quotes.

What is the difference between Plan G and Plan N?

Plan G has no visit copays and covers Part B excess charges. Plan N trades a lower premium for up to plan-specific amounts office copays, up to plan-specific amounts ER copays, and no excess-charge coverage.

Both plans cover the Part A deductible, hospital coinsurance, skilled nursing coinsurance, hospice coinsurance, blood, and foreign travel emergency at the same standardized levels. Both leave the Part B annual deductible to you if you became Medicare-eligible in 2020 or later. The visit copay and excess-charge differences are the entire gap between them.

Plan N makes sense when you see doctors infrequently and your providers accept assignment. Plan G makes sense when you generate enough visits that copays would eat the premium savings, or when a must-keep provider does not accept assignment.

Will my Medigap plan cancel if my health gets worse?

No. Guaranteed renewable policies stay in force regardless of claims or health changes. Premiums can still rise.

Federal law requires Medigap policies to be guaranteed renewable. A carrier cannot cancel your coverage because you got sick, filed a large claim, or developed a chronic condition. That protection is one of the main reasons people choose supplements over Advantage when they can afford the premium.

What can change is the premium itself. Carriers raise rates on age bands, policy pools, or entire blocks based on claims experience and state approval. A 6% annual increase on a supplement you have held for eight years is normal in some states. It is not a cancellation. It is a price adjustment.

Medical underwriting enters the picture when you apply for the first time outside open enrollment, or when you try to switch from Plan N to Plan G after your guaranteed-issue window closes. Underwriting can deny a new application. It cannot terminate coverage you already own.

Should I verify my doctors accept Original Medicare before buying Medigap?

Yes. Medigap only pays secondary to what Original Medicare covers, so non-participating providers can leave you with the full bill.

Call each must-keep office and ask whether they accept Medicare assignment for Medicare patients. Assignment means they agree to Medicare's approved rate as payment in full (plus whatever your supplement covers). Providers who opt out of Medicare entirely are outside the system. Medigap does not help there.

This check takes ten minutes and prevents the most common post-enrollment surprise I hear about: a supplement quote that looked perfect until the first claim from a non-participating specialist.

What Medigap never covers No Medigap policy pays for:

• Outpatient prescription drugs (Part D territory)
• Routine dental, vision, or hearing aids
• Long-term custodial nursing home care
• Services Medicare itself excludes as non-covered

You need a separate Part D plan for drugs unless other creditable coverage applies. Dental and vision are separate products or sometimes bundled on Advantage, not on supplements. Do not judge a Medigap policy for failing to include benefits federal law forbids it from covering.

Foreign travel emergency benefits are standardized on Plans G and N, generally 80% of emergency care abroad after a deductible, with a lifetime maximum. Useful if you cruise twice a year. Not the main reason most people buy supplements.

Your six-month open enrollment window Medigap open enrollment starts the month you turn 65 and enroll in Part B. It lasts six months. During that window, carriers must sell you any standardized plan they offer in your state without medical underwriting, regardless of health history.

Miss that window and you are generally subject to health questions on every new application. Some states have additional protections (guaranteed issue after Advantage trial periods, for example), but the six-month federal window is the cleanest path.

If you delayed Part B because of large-employer coverage, your Medigap open enrollment still starts when Part B starts, not when you turned 65. That nuance saves people who worked past 65 and assumed they missed their only shot.

How to shop carriers once the letter is chosen

After you pick Plan G or Plan N, the work is company selection.

Ask for:

1. Current premium at your age, zip, and tobacco status
2. Rating method, issue-age, attained-age, or community-rated
3. Household or spousal discount and what qualifies
4. Rate increase history in your state for that block over five to ten years
5. Whether the company is still selling the plan to new applicants

Two carriers with identical Plan G benefits can diverge by tens of dollars a month after a decade. The brochure shows today's premium. The rate history shows the curve.

Mutual of Omaha, UnitedHealthcare via AARP branding, Humana, Cigna supplement blocks, and regional mutuals all sell standardized letters in our licensed states, Florida, Alabama, Georgia, and North Carolina, but pricing and service differ. A carrier that closes new sales in your state still owes service on policies already in force.

Medigap versus the Advantage sales pitch

Advantage mailers win on monthly premium and extras. Medigap wins on predictability and access. Neither is free. You are choosing when you pay and how much friction sits between you and care.

If you want the full delivery-system comparison, use Advantage vs Original Medicare. For state-level pricing reality, use the Florida, Georgia, or Alabama comparison posts rather than re-reading a national overview.

Pre-existing conditions and waiting periods During Medigap open enrollment, pre-existing conditions cannot be used to deny you or price you up on guaranteed-issue applications. Outside that window, underwriting can decline the application or apply limited waiting periods depending on state and carrier rules.

Keep the policy documents. Guaranteed renewable status, rate letters, and the application copy are what you need if a billing dispute or future switch attempt comes up years later.

Next steps Learn product options on our Medigap page, compare paths with Medicare Supplement plans, and check official letters on Medicare.gov.

Schedule a consultation or call (850) 613-0057 for a no-cost carrier comparison in your state.

Licensed in Florida, Alabama, Georgia, and North Carolina. Independent, not tied to one carrier.

Plan availability, networks, drug formularies, and benefits vary by county and year. For all options in your area, contact Medicare.gov or 1-800-MEDICARE (TTY: 1-877-486-2048).