How Does Medicare Supplement Insurance Work?

Medicare Supplement Insurance, often called Medigap, is private health insurance that pays some of the costs Original Medicare does not cover. It works alongside Medicare Part A and Part B, not instead of them. When Medicare approves a claim and pays its share, the Medigap plan then pays part or all of what is left, depending on which lettered plan you bought.

That single idea explains almost everything about how these policies function. You keep Medicare as your primary coverage. The supplement sits behind it and fills specific gaps. It does not replace Medicare, and it does not work with Medicare Advantage plans.

How Does Medicare Supplement Insurance Work With Original Medicare?

Original Medicare pays first, and your Medigap plan pays second. This order is fixed by law and is the core of how the coverage operates.

Here is the sequence. You receive a covered service, such as a doctor visit or a hospital stay. Medicare processes the claim and pays its portion. The remaining amount, which may include deductibles, coinsurance, and copayments, gets sent to your Medigap insurer. The insurer then pays its share based on your plan letter.

Medicare Part A covers inpatient hospital care. Most people pay no premium for Part A because they paid Medicare taxes while working. Part B covers doctor visits, outpatient care, and certain medical equipment, and it charges a monthly premium.

Both parts leave you with cost-sharing. Part A has a deductible for each hospital benefit period. Part B has an annual deductible and then generally charges 20 percent coinsurance for most covered services. There is no annual out-of-pocket limit in Original Medicare itself. That missing cap is one of the main reasons people buy a supplement.

A Medigap plan does not add extra benefits like dental, vision, or hearing. Those are not part of standard Medigap coverage. It also does not cover long-term care, private-duty nursing, or prescription drugs. For drug coverage you need a separate Part D plan.

What Do the Different Medigap Plan Letters Cover?

Medigap plans come in standardized letters, from A through N. Federal law requires every insurer to offer the same benefits under the same letter, so a Plan G from one company covers the same things as a Plan G from another.

This standardization is unusual in insurance and worth understanding. The coverage is identical. What differs is the premium, the company’s customer service, and how it raises prices over time.

Plan F and Plan G are the most comprehensive options. Both cover the Part A deductible, the Part B deductible, and Part B coinsurance after you meet that deductible. The main difference is that Plan F also covers the Part B deductible itself. Plan F is generally closed to people who became eligible for Medicare after January 1, 2020, though some people who already had it can keep it.

Plan G is often the most comprehensive option available to newer Medicare enrollees. You pay the Part B deductible yourself, and after that the plan generally covers your remaining share of covered services.

Plan N covers most of the same ground but adds copayments for some office visits and emergency room visits, and it does not cover Part B excess charges. Those are amounts some providers may charge above what Medicare approves.

Plan A is the most basic. It covers Part A coinsurance and hospital costs, Part B coinsurance, and the first pints of blood. It does not cover the Part A or Part B deductible.

Plans B, C, D, K, L, and M fill in different combinations of these gaps. Plans K and L work differently from the others: instead of covering your full share, they pay a percentage and cap your annual out-of-pocket spending.

How Much Does Medigap Cost and How Is It Priced?

There is no single price for Medigap. Premiums vary widely by plan letter, insurer, and where you live.

Insurers use one of three pricing methods, and the method matters more than most buyers realize.

• Community-rated: Everyone in the area pays the same premium regardless of age. It may rise over time for everyone.
• Issue-age-rated: Your premium is based on your age when you buy the policy. It is generally lower the younger you enroll.
• Attained-age-rated: Your premium rises as you get older. This is often the cheapest at first and the most expensive later.

An attained-age policy can look like a bargain at 65 and become costly by 80. That is not a sales pitch. It is how the pricing structure is designed to work. Comparing plans on the first-year premium alone can lead to a decision you regret two decades later.

Other factors also affect what you pay. Tobacco use can raise premiums in many states. Some states restrict how insurers can price policies or limit when they can raise rates.

When Can You Enroll, and What Is Medical Underwriting?

Your best chance to buy any Medigap policy at the best price is during your Medigap Open Enrollment Period. This six-month window begins the first month you are 65 or older and enrolled in Medicare Part B.

During this window, insurers cannot deny you coverage or charge you more because of past or present health problems. This protection is one of the most important consumer rights in Medicare, and it is time-limited.

Outside that window, most states allow insurers to use medical underwriting. That means the company can review your health history, charge you more, or decline your application. A diagnosis of cancer, heart disease, or diabetes can lead to a denial in many states.

Some states have additional protections. A few require insurers to offer Medigap coverage to people under certain conditions, such as when a Medicare Advantage plan leaves the area or a person loses certain coverage. The rules vary by state, so the specifics depend on where you live.

If you have a health condition and you are past your initial window, your options may be limited. It is worth checking your state’s rules before assuming you cannot qualify.

Can You Have Medigap and Medicare Advantage at the Same Time?

No. A Medigap plan cannot be used with a Medicare Advantage plan, and it is generally illegal for an insurer to sell you one if you have Medicare Advantage.

The two work on completely different models. Medigap supplements Original Medicare. Medicare Advantage replaces Original Medicare with a private plan that often includes drug coverage and extra benefits, usually through a network of providers.

If you switch from Original Medicare to Medicare Advantage, you generally cannot use your Medigap policy. In most cases you would drop it. If you later want to return to Original Medicare, you may not be able to get your Medigap policy back without going through medical underwriting, unless you qualify for a special enrollment period.

This is a decision people often make casually and later regret. The ability to move back is not guaranteed.

What Medigap Does Not Cover

Understanding the limits matters as much as understanding the coverage. Medigap is not a broad health plan.

It does not cover prescription drugs. You need a separate Part D plan for that, and Part D has its own premiums, deductibles, and coverage rules.

It does not cover long-term care, which includes most nursing home care and help with daily activities like bathing and dressing. Some Medicare coverage for skilled nursing care is short-term and tied to a hospital stay, and Medigap may help with cost-sharing for that, but it does not pay for ongoing custodial care.

It does not cover routine dental, vision, or hearing care. It does not cover private-duty nursing. It does not cover care received outside the United States, though a few plan letters include limited foreign travel emergency coverage.

Medigap also does not cover services that Medicare itself does not cover. If Medicare denies a service as not medically necessary, the supplement generally will not pay either.

Frequently Asked Questions