What Is a Medicare Supplement (Medigap) Plan?

The short answer: A Medicare Supplement — Medigap — is a private policy that works alongside Original Medicare and pays most of what Medicare leaves behind: deductibles, coinsurance, and that uncapped 20% of doctor and outpatient costs. Plans are standardized by letter, so a Plan G is a Plan G no matter which company sells it — the coverage is identical and only the price and the company differ. It is the “predictability” path through Medicare.

The name explains the job. Original Medicare has gaps — real ones, with no annual limit on what they can add up to — and these policies were built to fill them. Here is how they work, what the letters mean, and the one enrollment fact that matters more than all the rest.

What does a Medigap plan actually do?

When you have Original Medicare plus a Medigap policy, your care flows like this: you see any doctor or hospital in the country that accepts Medicare — no networks, no referrals. Medicare pays its share first. Then your Medigap plan pays its share of what is left, automatically, because claims cross over from Medicare to your supplement without you filing anything.

What lands on you is whatever small piece your particular plan letter leaves in place. On the popular plans, that remainder is modest and — more importantly — predictable. The uncapped 20% problem disappears. A hard health year stops being a hard financial year.

Two more traits people value once they understand them: Medigap policies are guaranteed renewable — as long as premiums are paid, the company cannot cancel the policy or trim its benefits because your health changed. And because the plan follows Medicare rather than a network, moving or traveling within the U.S. does not break your coverage.

Why are the plans named with letters?

Federal standardization. Every Medigap plan letter — A, B, C, D, F, G, K, L, M, N — is defined by law, and every company selling that letter must provide exactly those benefits. This is unusual in insurance, and it works in your favor: comparing plans becomes a genuine apples-to-apples price comparison instead of a fine-print hunt.

In practice, most people shopping today land on two letters. Plan G is the most comprehensive option available to people newly eligible for Medicare — after you meet the annual Part B deductible, it covers essentially everything Medicare approves. Plan N trades a lower premium for small copays and one coverage difference. The trade-offs between them deserve their own discussion: Plan G vs Plan N, compared honestly.

(If you have heard of Plan F: it covered even the Part B deductible, but it closed to anyone who became eligible for Medicare after January 1, 2020. People who already have it may keep it.)

What does a Medigap plan cost?

Premiums vary by plan letter, your age, your ZIP code, tobacco use, and the company’s pricing method — which is exactly why the standardization matters. Two companies can charge meaningfully different premiums for the letter-for-letter identical policy. Shopping the same letter across companies is where an independent agent earns their keep, since the agent is paid by the carrier either way and your premium is the same with or without one.

One structural note worth asking about when you shop: companies price policies using different rating methods, and two identical premiums today can age very differently over the next decade. This is the kind of detail that rarely appears in an online quote engine.

The six-month window that changes everything

Here is the fact that outranks every other detail on this page. When your Part B starts and you are 65 or older, a six-month Medigap open enrollment period begins — and during it, companies must sell you any plan they offer, without medical questions, at the same price a healthy person pays.

After those six months, in most situations, applying for a Medigap policy means medical underwriting: health questions, and the possibility of being charged more or declined. A diagnosis at 68 can quietly close a door that stood wide open at 65. Georgia may offer additional protected situations, and there are federal guaranteed-issue rights in specific circumstances — losing employer coverage, a plan leaving your area — but the six-month window is the one everyone gets and the one you should never spend by accident.

This is why “I’ll just start with the cheapest thing and upgrade later” is the single most expensive sentence in Medicare planning. Later has conditions attached. The full timeline, including this window, is in the Medicare timing guide.

What a Medigap plan does not do

Honesty requires the other side of the ledger:

• No drug coverage. Medigap pairs with a standalone Part D plan — that is a separate, small decision made alongside it.
• No routine dental, vision, or hearing. Original Medicare does not cover those, so a supplement to Original Medicare does not either. Standalone policies exist for that job.
• A real monthly premium. The predictability is paid for monthly. For some budgets and situations, a Medicare Advantage plan is the better structural fit — that comparison deserves an honest look rather than a slogan.

Common questions about Medicare Supplements

What is the difference between Medigap and Medicare Advantage?

A Medigap plan works with Original Medicare — Medicare stays your primary coverage and the supplement fills its gaps, with no network. A Medicare Advantage plan replaces the delivery of your Medicare benefits with a private plan, usually with a network, copays as you go, and often built-in drug coverage. You can hold one or the other, never both.

Can I be turned down for a Medicare Supplement?

During your six-month open enrollment window — which starts when Part B begins at 65 or later — no. Companies must accept you without health questions. Outside that window, in most circumstances, yes: applications can go through medical underwriting, and health history can affect the price or the answer. Certain situations restore guaranteed rights, so it is always worth asking before assuming.

Does a Medigap plan cover my spouse too?

No — Medicare and Medigap are individual coverage. Each spouse enrolls separately, each with their own plan and premium. Some companies offer a household discount when both spouses hold policies, which is one of those quiet details worth checking when comparing prices.

Do I need to change my Medigap plan every year?

No. Unlike drug plans, Medigap benefits do not change from year to year — a Plan G stays a Plan G. The annual fall enrollment season on television is mostly about Part D and Medicare Advantage. A periodic price check every few years is sensible; an annual scramble is not required.

The simple version

Medigap is the predictability path: Original Medicare’s freedom to see any doctor who accepts Medicare, with the gaps filled and the surprises removed, in exchange for a monthly premium. The letters are standardized, so shopping is really about price and company. And the six-month window at the start is when every door is open — the parts of Medicare guide shows where it fits in the bigger picture, and the Turning-65 Checklist keeps the timing straight.

Wondering what this looks like for your situation? Call or text 770-765-7007 — plain-language answers at no cost, and someone who’s still there after you enroll. We’re based in Cumming, Georgia, working with families across North Georgia — and licensed in states across the country, so distance never gets in the way.