What Is Medigap? Medicare Supplement Insurance Explained

Original Medicare pays for a large share of your hospital and doctor bills, but it does not pay all of it. There is no annual cap on what you might owe out of pocket, and the deductibles and the 20 percent coinsurance on Part B can add up fast if you have a serious year. Medigap, which is the common name for Medicare Supplement Insurance, is the private insurance you can buy to cover those leftover costs. Think of it as a second layer that sits on top of Original Medicare and pays its share after Medicare pays first.

The idea is simple, but the details trip people up because there are ten different versions, they are named with letters, and the single most important decision about pricing happens in a six month window most people only hear about once. Here is how the whole thing works, in plain terms, with the 2026 figures that matter.

What Medigap actually does

When you have Original Medicare, meaning Part A for hospital care and Part B for doctor and outpatient care, Medicare pays its portion of a covered service and then you are responsible for the rest. That rest can include the Part A hospital deductible, the Part B annual deductible, coinsurance, and copayments. A Medigap policy steps in and pays some or all of those gaps, depending on which plan you chose.

A few ground rules apply to every Medigap policy. You can only buy one if you have Original Medicare, so you generally need both Part A and Part B in place first. A Medigap policy covers only one person, so a married couple who both want coverage each buy their own policy. And you pay a monthly premium for Medigap on top of your Part B premium, which is the standard cost of being in Medicare in the first place. Medigap does not replace Part B, it works alongside it.

The feature people value most is predictability. Instead of wondering what a hospital stay or a run of specialist visits will cost, a strong Medigap plan turns most of your medical bills into a known monthly premium plus very little else. That tradeoff, a higher fixed cost in exchange for fewer surprises, is the heart of the decision.

The ten standardized plans, named by letter

In most states, Medigap policies are standardized, which is the most helpful thing to understand about them. The federal rules define ten plan types, labeled with letters: A, B, C, D, F, G, K, L, M, and N. Because the benefits inside each letter are set by law, a Plan G from one insurance company covers the exact same things as a Plan G from any other company. The coverage does not change based on which brand name is on the card or which state you live in.

That has a very practical consequence. If two companies both sell Plan G, the only meaningful difference between them is price and service, not coverage. So the apples to apples way to shop is to gather several quotes for the same plan letter and version, then weigh them against each insurer's service record and financial stability. Just be sure you are comparing the same version, since a few plans also come in a high-deductible flavor that is not the same product, and comparing a Plan G to a Plan N is comparing two different coverage levels, not two prices for the same thing. Medicare's own Medigap plan finder on Medicare.gov lets you search the policies sold in your area and line up the same plan letter from several insurers, which keeps the comparison honest.

Every company that sells Medigap at all must offer Plan A. Beyond that, if they offer more plans they must also offer a benchmark plan for each group of enrollees. The table below shows how the most common letters stack up on the benefits people ask about most. It reflects the standard versions of each plan, and note that the hospital benefit includes up to 365 extra days of coverage after your Original Medicare hospital benefits are used up.

The two plans most people actually choose

Out of the ten letters, the conversation for most new enrollees comes down to two: Plan G and Plan N. Both are available to people who are new to Medicare, and both offer broad coverage.

Standard Plan G is the most comprehensive plan available to new enrollees. After you pay the annual Part B deductible, which is 283 dollars in 2026, standard Plan G picks up essentially everything else that Original Medicare leaves behind, including the Part A deductible, the 20 percent Part B coinsurance, Part A hospital costs for up to 365 additional days after your Original Medicare hospital coverage is used up, skilled nursing coinsurance, and even the excess charges some doctors add when they do not accept Medicare assignment. For many retirees who want the fewest surprises, standard Plan G is the default answer.

One wrinkle is worth naming before you shop, because it changes the math completely. There is also a high-deductible version of Plan G, and it does not pay after the small Part B deductible the way the standard version does. With high-deductible Plan G you pay for Medicare-covered costs out of your own pocket until you reach a yearly deductible, which is 2,950 dollars in 2026, and only then does the plan start paying. The 283 dollar Part B deductible counts toward that 2,950 rather than sitting on top of it. In exchange for that larger upfront exposure, high-deductible Plan G usually carries a much lower monthly premium. So the clean statement that Plan G pays everything after the Part B deductible is true for standard Plan G, not for the high-deductible version. If a Plan G quote looks surprisingly cheap, check whether it is the high-deductible plan before you assume you found a bargain.

Plan N covers almost as much as standard Plan G but asks you to share a little more of the day to day cost in exchange for a usually lower premium. With Plan N you pay a copayment of up to 20 dollars for some office visits and up to 50 dollars for an emergency room visit that does not lead to being admitted. Plan N also does not cover Part B excess charges, so it can matter whether the doctors in your area accept Medicare assignment. For people who do not expect heavy use and want to save on premiums, Plan N is a reasonable middle path.

The other letters serve narrower needs. Plan A is the required baseline with the thinnest coverage. Plans B, D, and M fall in between and are less commonly sold. The right letter depends on how much risk you want to hand off versus how much premium you want to pay, and there is no universally correct answer.

Why you may never see Plans C and F

If you read older articles, you will see Plan F described as the gold standard, because it covered the Part B deductible too and left the enrollee with almost nothing to pay. That is still true for people who already had it. But there is a cutoff that matters for anyone newer to the program.

If you were new to Medicare on or after January 1, 2020, you cannot buy Plan C or Plan F. The reason is a rule that bars newer Medigap plans from covering the Part B deductible. People who were already eligible for Medicare before that date can still buy or keep C and F, but for most of today's new retirees those two letters are simply off the menu. This is why standard Plan G has quietly become the new top choice: it is essentially Plan F minus the one small deductible that newer plans are not allowed to cover.

Plans K and L, and the out-of-pocket cap

Two letters work differently from the rest. Plans K and L do not pay 100 percent of most gaps. Instead, Plan K pays 50 percent and Plan L pays 75 percent of several cost categories, such as the Part A deductible, Part B coinsurance, blood, and skilled nursing coinsurance. In return, they carry something the other plans do not: an annual out-of-pocket limit.

For 2026, once you reach the yearly out-of-pocket limit and have met the Part B deductible, the plan pays 100 percent of covered services for the rest of the calendar year. That limit is 8,000 dollars for Plan K and 4,000 dollars for Plan L in 2026. These plans appeal to people who want a lower premium and are comfortable sharing costs up to a ceiling, knowing the ceiling exists. The chart below shows a hypothetical year to make the tradeoff concrete.

The six month window that protects your enrollment rights

If you remember only one thing about Medigap, make it this. Under federal law you get a one time, six month Medigap Open Enrollment Period. It starts on the first day of the month you are both 65 or older and enrolled in Part B. During those six months you have the strongest buying rights you will ever have.

Inside that window, an insurance company cannot refuse to sell you any Medigap policy it offers and cannot charge you more because of a pre-existing condition. A company may still ask health questions on the application, and Medicare's buying guide tells you to answer them. The key protection is that during this window the insurer cannot use your answers to deny you a policy it sells or charge you more because of your health. This is called guaranteed issue: your health history does not change whether you get the policy or what you pay at the start. It protects your acceptance and your opening price, not the premium forever, since premiums can still rise over time. One narrow exception, covered next, can delay when coverage begins for a condition you already had, but not whether you are accepted or what you first pay. For someone with a chronic condition, this window can be the difference between affordable coverage and being priced out or turned away entirely.

That caveat turns on something called prior creditable coverage. A company can apply a pre-existing condition waiting period of up to six months before it covers costs tied to a condition you already had. If you had at least six months of continuous creditable coverage before you enrolled, that waiting period generally disappears entirely. Shorter prior coverage does not erase the waiting period, but it can shrink it, roughly month for month. Timing also matters here: a break in your earlier coverage of more than 63 days can mean that coverage no longer counts toward reducing the wait. Once the six month window itself closes, the rules flip. Outside of open enrollment, in most states a company can use medical underwriting, which means it can review your health, charge you more, or deny you a policy altogether. The steps below show how the timing usually unfolds.

Guaranteed issue rights outside the window

The six month window is not the only time your health is protected, but the other times are specific. Certain situations create what are called guaranteed issue rights, also known as Medigap protections. When you have one, a company must sell you a policy, must cover your pre-existing conditions without a waiting period, and cannot charge you more because of your health history.

These rights tend to show up around involuntary changes, such as losing coverage you were counting on, a Medicare Advantage plan leaving your area or ending its contract, or a trial right after trying Medicare Advantage for the first time. The exact list and time limits are defined by federal rule, and some states add broader protections of their own. The practical takeaway is that guaranteed issue rights are usually tied to a triggering event and come with a deadline, often an application window that closes 63 days after your old coverage ends, so if one applies to you, act quickly rather than assuming the door stays open.

What Medigap does not cover

Medigap is narrow on purpose. It fills the gaps in Original Medicare, and that is nearly all it does. It generally does not cover prescription drugs, which is why people with Medigap usually add a separate Part D drug plan. You can read more about how that layer works in our guide to Medicare Part D drug coverage.

Medigap also does not cover long-term care such as non-skilled help in a nursing home, routine dental care, vision, hearing aids, or private-duty nursing. Those are real expenses in retirement, and the fact that Medigap skips them is one reason planning for health costs needs more than a single policy. If you are mapping out the bigger picture, our overview of Medicare basics for retirement planning walks through the pieces that fit together.

How companies price the same coverage differently

Because benefits inside a letter are identical, price is where companies compete, and they do not all set prices the same way. Three pricing methods are common, and knowing which one a policy uses tells you how your premium is likely to move over time.

• Community-rated: everyone with that policy pays the same premium regardless of age. Your premium can still rise with inflation, but not simply because you got older.
• Issue-age-rated: your premium is based on your age when you bought the policy. Buy younger and the starting price is lower, and it does not increase just because you age.
• Attained-age-rated: your premium is based on your current age and climbs as you get older. These often start cheapest and can become the most expensive later.

Two policies with the same letter and a similar starting quote can diverge a lot over twenty years depending on which method they use. A low attained-age quote at 65 may look like a bargain and then rise steadily into your late seventies. On top of that, even a premium that held perfectly level would stretch less each year, because inflation quietly shrinks what every dollar buys, so your retirement income has to keep pace with rising costs. One way some retirees prepare for climbing premiums, along with the dental, vision, and other costs Medigap does not touch, is to set aside a small savings cushion early. The tool below is not a premium forecast or a promise of any return. It simply shows how a starting amount plus steady monthly saving might grow at an assumed rate, so you can picture the effect of putting money aside for future costs.

Medigap or Medicare Advantage

Medigap and Medicare Advantage are two different roads, and they are not built to be driven at the same time. A Medigap policy only does its job alongside Original Medicare, and it is illegal for a company to sell you a new Medigap policy while you are enrolled in a Medicare Advantage plan. That prohibition is not a flat wall, though. If you are leaving Advantage to return to Original Medicare, you are allowed to buy a Medigap policy, as long as your Advantage coverage ends before the Medigap coverage begins.

Two separate questions decide how smoothly that goes: when you are allowed to drop Advantage, and whether a company can weigh your health when you apply for Medigap. The first runs on Medicare's own calendar, through periods such as the fall Medicare Open Enrollment and the Medicare Advantage Open Enrollment Period early in the year. Those disenrollment periods control the switch back to Original Medicare, but they do not by themselves require a Medigap company to accept you. That turns on whether you have a guaranteed issue right. The most common is a trial right: if you joined Advantage when you first became eligible at 65, or you dropped a Medigap policy to try Advantage for the first time, you generally have a one time right to switch back within your first 12 months and buy Medigap on a guaranteed issue basis. Certain coverage losses, such as your Advantage plan leaving your area or ending its contract, create the same protected right, with an application window running from 60 days before your coverage ends to no more than 63 days after. Outside those cases, a voluntary return to Original Medicare usually comes with no guaranteed issue window, so in most states your Medigap application is then subject to medical underwriting, meaning the company can review your health, charge more, or turn you down, and the policy still cannot start until the Advantage plan stops.

There is also a subtle distinction about policies you already hold. If you already owned a Medigap policy and then joined a Medicare Advantage plan, you are legally allowed to keep it, but it cannot pay your Advantage plan's copayments, deductibles, or premiums. In practice you would be paying a Medigap premium for coverage you cannot use, which is why many people drop it when they move to Advantage.

Beyond those rules, the two approaches simply work differently. Medigap pairs with Original Medicare and a standalone drug plan, usually offering wide provider access and predictable costs in exchange for higher premiums. Medicare Advantage bundles coverage through a private plan, often with a low or no premium and extra perks, but with networks and an out-of-pocket structure that varies by plan. The choice is less about which is better and more about which fits how you use care and how much certainty you want. We compare the two paths in detail in our guide to Medicare versus Medicare Advantage.

Three states that play by their own rules

The standardized letter system covers most of the country, but not all of it. Massachusetts, Minnesota, and Wisconsin standardize their Medigap policies differently and do not use the same A through N framework. If you live in one of those states, the core idea still holds, meaning policies are standardized and benefits are defined, but you will compare plans using that state's own system rather than the national letters. It is worth confirming the local structure before you shop so you are comparing the right things.

Changing your mind later

You are not permanently locked into the first policy you buy, but changing later is not always easy. You can apply for a different Medigap policy at any time, yet outside a protected window the new company can review your health and decide whether to accept you and at what price. If you are healthy, switching to a better price or a different letter can work smoothly. If your health has changed, underwriting can stand in the way.

Some people use the early years of retirement, when they are often healthiest, to lock in coverage, then reassess only if a clearly better option appears and they can still pass underwriting. Others in states with annual switching protections have more freedom. The key is to never assume that dropping a Medigap policy is reversible, because getting back in can be harder than getting out.

Putting it together

Medigap is one of the more learnable corners of retirement, precisely because the plans are standardized. Once you understand that the letters define fixed benefits, that price is the real variable, and that your six month open enrollment window is when your health cannot be held against you, the rest is a matter of matching a plan to how you want to trade premium against risk. Standard Plan G and Plan N cover most people's needs, high-deductible Plan G trades a larger yearly deductible for a lower premium, Plans K and L add an out-of-pocket ceiling, and the plans that cover the Part B deductible are closed to most new enrollees.

None of this is a guarantee about access, cost, or any particular outcome, because premiums, availability, and state rules all vary and change over time. But the structure is stable, and the decision rewards attention at the right moment. If you are approaching 65, mark the start of your Part B coverage on the calendar, because the clock on your best buying rights starts the same day.