Supplemental insurance fills gaps that Original Medicare leaves open, but whether you need it depends on your health, income, and how much out-of-pocket cost you can handle

Original Medicare covers a lot, but not everything. You pay a share of hospital costs, a share of doctor visits, and all prescription drug costs unless you add a separate drug plan. Supplemental insurance (also called Medigap) picks up some or all of those costs you would otherwise pay yourself. It is not required, and many people do fine without it — but if you have chronic conditions, take multiple medications, or see doctors regularly, the monthly premium often costs less than what you would pay out-of-pocket anyway.

The real question is not whether supplemental insurance exists, but whether the premium you would pay is worth what it saves you. That math is different for everyone, and it changes if your health or income changes.

Key Takeaways

  • Original Medicare requires you to pay a deductible, coinsurance, and copays for hospital stays, doctor visits, and outpatient services — supplemental insurance covers some or all of these costs.
  • Prescription drugs are not covered by Original Medicare at all, so you need a separate Part D plan; supplemental insurance does not cover drugs.
  • You can enroll in supplemental insurance within 63 days of turning 65 and enrolling in Part B without medical underwriting, but after that window closes, insurers can deny you or charge more based on your health history.
  • If your income is below certain thresholds, you may be better served by Medicaid or a Medicare Advantage plan with low or zero premiums than by paying supplemental premiums out of pocket.
  • The 10 standardized Medigap plans (A through N) offer different levels of coverage at different prices, so comparing plans from multiple insurers in your area is the only way to find the best rate.

What Original Medicare actually costs you

To know whether supplemental insurance makes sense, you need to see what you are paying now. In 2024, Original Medicare Part A (hospital insurance) has a $1,676 deductible per hospital stay. After you meet that, you pay coinsurance — a percentage of the bill — for days 61 through 90 of a hospital stay, and even more per day if you stay longer than 90 days. For a two-week hospital stay, that can easily add up to thousands of dollars.

Part B (doctor and outpatient services) has a $240 annual deductible, then you pay 20 percent of the approved amount for most services after that. If you see a specialist, have lab work done, or need imaging, those 20 percent shares stack up fast. A single MRI can cost $300 to $500 out of your pocket. A course of physical therapy — three times a week for six weeks — can run $1,200 to $2,400 depending on where you live.

These numbers vary by year and by service, but the pattern is the same: Original Medicare covers the bulk of the bill, but you cover a meaningful slice. Supplemental insurance exists to cover that slice.

The 10 Medigap plans and what each one covers

There are 10 standardized supplemental plans, labeled A through N. They are standardized by federal law, which means Plan A from one insurance company covers exactly the same things as Plan A from another. The only difference is price. This is important: you are not comparing coverage when you shop — you are comparing which insurer charges the least for the same coverage.

Plan A is the most basic and least expensive. It covers your Part A coinsurance (the hospital cost-sharing) and your Part B coinsurance (the 20 percent you pay for doctor visits and outpatient care). It does not cover your deductibles. Plan G is the most comprehensive and most expensive. It covers almost everything except your Part B deductible. Plans B through F and H through N fall in between, each covering a different combination of deductibles, coinsurance, and copays.

The plan that makes sense for you depends on how much you can afford to pay in premiums and how much you can afford to pay out-of-pocket when you need care. If you are healthy and rarely see a doctor, Plan A might be enough. If you have multiple chronic conditions and see specialists regularly, Plan G might save you money overall even though the premium is higher.

When you can enroll without medical questions

The timing of when you enroll in supplemental insurance matters enormously. If you enroll within 63 days of turning 65 and enrolling in Medicare Part B, insurers must sell you any Medigap plan you choose at the standard rate — they cannot ask about your health, deny you, or charge you more because you have diabetes or heart disease. This window is called open enrollment, and it is the only time most people get may provide access to all plans.

If you miss that 63-day window, you enter what is called the general enrollment period. At that point, insurers can underwrite you — meaning they can ask about your medical history, deny your process, or charge you a higher premium based on your health conditions. Some states have protections that limit how much more they can charge, but others do not. In some cases, an insurer can straightforward refuse to sell you a plan at all.

This is why timing matters so much. If you are turning 65 soon, marking your calendar for the 63-day window is one of the most important financial decisions you will make in retirement.

Supplemental insurance versus Medicare Advantage

You cannot have both supplemental insurance and a Medicare Advantage plan at the same time. If you choose Original Medicare, you can add supplemental insurance. If you choose a Medicare Advantage plan (Part C), you do not need supplemental insurance because the Advantage plan itself handles the cost-sharing.

Many Medicare Advantage plans have zero monthly premiums and lower out-of-pocket maximums than supplemental insurance would cost. However, they usually require you to use doctors and hospitals in their network, and they often require prior authorization before you can see a specialist or have a procedure. If you travel frequently or have a strong relationship with doctors outside a particular network, Original Medicare plus supplemental insurance gives you more freedom.

The choice between these two paths is not about which is objectively better — it is about which trade-off fits your life. Advantage plans trade network restrictions for lower upfront costs. Original Medicare plus supplemental insurance trades higher premiums for more choice and predictability.

Income-based help if premiums are too high

If your income is low enough, you may be better served by Medicaid than by paying supplemental premiums. Medicaid rules vary by state, but in many states, Medicaid will pay your Medicare premiums and cost-sharing if your income falls below a certain threshold. This is called Medicare Savings Programs or Medicaid Buy-In, depending on your state.

To find out whether you may have access to, contact your state Medicaid office or call 211 and ask for Medicare Savings Programs in your area. The income limits vary by state and change each year, but if you are living on a small Social Security check, it is worth checking. You may also be able to get help paying for prescription drugs through the Low-Income Subsidy program, which is separate from supplemental insurance.

How to compare and choose a plan

Start by deciding which of the 10 Medigap plans fits your health needs and budget. If you are not sure, Plan G is the most popular because it covers nearly everything except the Part B deductible, which is manageable. Plan A is the cheapest entry point if you want to keep premiums low.

Once you have picked a plan letter, get quotes from at least three insurers in your area. You can do this by visiting Medicare.gov and using their Medigap plan finder, or by calling insurers directly. Prices vary significantly by company and by region — the same Plan G might cost $120 a month from one insurer and $180 from another. Getting quotes takes 20 minutes and can save you hundreds of dollars a year.

After you enroll, your premium will likely increase each year. Some insurers use age-based rating, which means your premium goes up as you get older. Others use issue-age rating, which means your premium is locked to the age you were when you enrolled and stays lower longer. Ask about the rating method when you get your quote — it affects your long-term costs.

What supplemental insurance does not cover

Supplemental insurance covers cost-sharing (deductibles, coinsurance, copays) for services that Original Medicare covers. It does not cover services Medicare does not cover — things like dental, vision, hearing aids, or long-term care. It also does not cover prescription drugs. If you take medications, you need a separate Part D prescription drug plan, which you can add to Original Medicare at any time.

Some people think supplemental insurance is a catch-all, but it is narrowly focused on filling the gaps in Original Medicare's cost-sharing. If you need dental work or hearing aids, you will need to pay out of pocket or look into separate dental and vision plans, which are sold by private insurers and are not part of Medicare.

Frequently Asked Questions

Can I switch Medigap plans after I enroll?

Yes, you can switch plans, but the rules depend on when you switch. During your first 12 months of enrollment in a Medigap plan, you have a may provide right to switch to any other plan without medical underwriting. After that, you can still switch, but the new insurer can underwrite you and charge more based on your health. Switching is usually only worth it if you find a significantly lower price for the same coverage.

What happens if I do not enroll in supplemental insurance during the 63-day window?

You can still enroll later, but insurers can ask about your health and deny you or charge you more. Some states have protections that limit the extra charge, but others do not. In the worst case, an insurer can refuse to sell you a plan. This is why enrolling during the open window is so important — it is the only time you have may provide access at standard rates.

Do I need supplemental insurance if I have a Medicare Advantage plan?

No. Medicare Advantage plans include their own cost-sharing structure and out-of-pocket maximum, so supplemental insurance is not allowed with Advantage plans. You choose either Original Medicare plus supplemental insurance, or a Medicare Advantage plan on its own.

Will my supplemental insurance premium go up every year?

Yes, almost certainly. Premiums increase due to inflation and rising healthcare costs. How much they increase depends on the insurer and the rating method they use. Some insurers raise rates more steeply than others, which is why comparing prices every year or two is worth doing — you may find a better rate elsewhere.

Can I use my supplemental insurance at any doctor or hospital?

Yes. Supplemental insurance works with Original Medicare, which means you can go to any doctor or hospital that accepts Medicare. There are no network restrictions like there are with Medicare Advantage plans. This is one of the main reasons people choose Original Medicare plus supplemental insurance over Advantage plans.