Medicare Supplement Plans Explained

Someone leaving a hospital bill asks: what is a medicare supplement plan? It is Medigap insurance that pays the deductibles, copayments and coinsurance left after Original Medicare pays, and it is easiest to buy in a one-time six-month window.

Medigap fills specific gaps in Original Medicare and nothing beyond them. The sections below correct the most common misunderstandings, and disputes that arise after care are covered in what to do when insurance denies a claim.

What Medigap pays for and what it leaves out

Medigap pays part or all of the out-of-pocket costs that remain once Medicare has paid its share. One enrollment guide lists deductibles, copayments and coinsurance as the expenses you otherwise shoulder yourself. Some plan types also cover Part B excess charges and emergency overseas health coverage, so the benefits differ by plan letter.

A concrete gap is the annual Part B deductible, which one enrollment guide puts at $283 in 2026. The same guide gives the standard Part B premium as $202.90 per month for most enrollees. Medigap does not replace that premium, because Part B must already be in place before a Medigap policy can be bought.

Three misreadings cause most of the confusion:

• Medigap is not a stand-alone policy. Buying requires Original Medicare, meaning Part A (hospital insurance) and Part B (medical insurance).
• Medigap is not a network plan. Supplement plans have no required provider networks, so any doctor who accepts Medicare is open to you.
• Medigap is not complete coverage. Supplement plans generally exclude Part D prescription drugs, dental, vision, hearing aids and long-term care.

The contrast with Medicare Advantage shows where Medigap sits in the wider choice.

Figures and descriptions in the table come from a supplement-plan guide and Healthline’s Medicare overview.

Do you need Medigap?

Medigap is an add-on that has to be bought, and it only works alongside Original Medicare. Whether it earns its monthly premium depends on how much leftover cost you could absorb, because Medicare’s deductibles and coinsurance do not disappear without it.

The plan suits people who want to stay in Original Medicare and keep the freedom to see any doctor accepting Medicare. It suits them less if a lower monthly premium and bundled extras matter more than that freedom, since Medigap usually costs more per month than Medicare Advantage. Leftover balances that go unpaid raise a separate question: do medical bills affect credit score.

Medigap and Medicare Advantage do not combine

Medigap cannot be held alongside Medicare Advantage. Medicare Advantage plans provide your Part A and Part B benefits themselves, while Medigap requires Original Medicare to sit on top of. Choosing one means setting the other aside.

Guaranteed issue rights, also called Medigap protections, let you enroll without medical underwriting in set circumstances. One such trigger is when your Medicare Advantage plan leaves your service area or ends. Anyone considering a move from Medicare Advantage to Medigap should check whether a protection applies before giving up the current plan.

Standardized plan letters

Medigap plans are standardized by letter, and plans with the same letter offer the same basic benefits no matter where you live. The ten letters are A, B, C, D, F, G, K, L, M and N. That means comparing one letter across insurers is a comparison of price and service, not of core coverage.

Plan G shows how this works. It covers everything except the annual Part B deductible, which is $283 in 2026. Features such as Part B excess charges and overseas emergency care appear only on some plan types, so check the specific letter before choosing it.

The Medigap open enrollment period

The Medigap open enrollment period lasts six months and comes only once. It starts the first day of the month you are 65 and have Medicare Part B. It does not repeat every year.

Timing matters for both acceptance and price. During the window, the insurance company can’t deny you coverage due to pre-existing health problems. After it closes, you may not be able to buy a plan, or it may cost more. Most states may require medical questions and underwriting at that point, so the safest approach is to treat the start month as the deadline to compare quotes, not the end of the window.

Medigap costs and why prices differ

Prices vary because insurers set premiums in different ways and because states differ. For the same Plan G coverage, one enrollment guide found the most expensive carrier charging $100 to $240 a month more, depending on the state, based on July 2026 filed rates. Because the benefits are identical by letter, that gap is purely a price difference, so quotes from several insurers are worth requesting.

The pricing method matters as much as today’s quote.

The three methods are described in Healthline’s Medicare supplement guide.

Frequently asked questions