A Medicare Supplemental Plan Fills the Gaps That Original Medicare Leaves

Medicare Supplemental Insurance, also called Medigap, is a policy sold by private insurance companies that pays for costs that Original Medicare (Parts A and B) does not cover. Original Medicare covers a large share of hospital and doctor bills, but leaves you responsible for deductibles, copayments, and coinsurance. A Medigap policy picks up some or all of those out-of-pocket costs, depending on which plan you choose.

Medigap is separate from Medicare Advantage (Part C), which is an alternative way to receive Medicare benefits through a private plan. With Medigap, you keep Original Medicare and add a supplemental policy on top. You can see any doctor or hospital that accepts Medicare, and your Medigap policy works alongside your Medicare coverage.

Key Takeaways

  • Medigap policies are standardized by the federal government into ten lettered plans (A through N), so Plan G from one insurer covers the same things as Plan G from another.
  • You can only buy Medigap during specific windows: within six months of turning 65 and enrolling in Medicare Part B, or during your state's annual open enrollment period.
  • Medigap premiums vary by insurer, age, and location, and some insurers use "issue-age" pricing (based on your age when you buy) while others use "attained-age" pricing (increases as you get older).
  • You must have Original Medicare Parts A and B to buy Medigap; you cannot combine it with Medicare Advantage.
  • The most popular plans are G and N because they cover most out-of-pocket costs at a reasonable premium, though Plan A is the cheapest entry point.

The Ten Standardized Medigap Plans and What Each Covers

The federal government defines ten Medigap plans, labeled A through N. Each plan covers a fixed set of services, so the coverage is identical no matter which insurance company sells it to you. The differences are in what they pay for and how much you pay in premiums.

Plan A is the most basic and least expensive. It covers the Part B deductible, coinsurance for hospital stays, and some skilled nursing facility costs, but does not cover the Part A deductible or prescription drugs. Plan G covers nearly everything Plan A does, plus the Part A deductible, and is the most comprehensive option available today. Plan N is similar to G but requires you to pay a small copayment at the doctor's office and emergency room, which keeps the premium lower.

Plans B, C, D, F, H, I, J, K, and L each cover different combinations of deductibles, coinsurance, and other costs. Plan F was the most comprehensive option before 2020 but is no longer sold to people newly turning 65. If you already had Plan F before 2020, you can keep it. The plan you choose depends on your budget and how much out-of-pocket risk you want to carry yourself.

When You Can Buy Medigap and Why Timing Matters

You have the strongest protection when you buy Medigap during your Medigap Open Enrollment Period, which runs for six months starting the first day of the month you turn 65 and enroll in Medicare Part B. During this window, insurance companies cannot deny you coverage or charge you more based on your health history — a protection called may provide issue.

If you miss this window, you can still buy Medigap during your state's annual open enrollment period, which typically runs from October 15 to December 7 each year. Outside these windows, insurers can refuse to sell you a policy or charge you a higher premium if you have a pre-existing condition. Some states have additional protections that extend may provide issue beyond the federal minimum, so check your state's rules.

The timing also matters if you are switching from Medicare Advantage to Original Medicare. You have 63 days from the date your Medicare Advantage plan ends to buy Medigap with may provide issue. If you wait longer, you lose that protection and may face denial or higher costs.

How Medigap Premiums Work and What You Will Pay

Medigap premiums vary widely by plan, insurer, age, and where you live. There is no single "cost" for Plan G or Plan A — you must get quotes from multiple insurers to find the lowest price in your area. Premiums also depend on the pricing method the insurer uses.

Issue-age pricing bases your premium on your age when you first buy the policy. Your premium stays lower than it would under other methods, but only if you lock in a policy early. Attained-age pricing increases your premium every year as you get older, so your cost rises over time. Community-rated pricing charges everyone in your state the same premium regardless of age, which can be cheaper for older adults but more expensive for younger retirees.

Most insurers also offer discounts for paying annually instead of monthly, or for setting up automatic payments. Some states regulate how much insurers can increase premiums year to year, so your state's rules affect your long-term costs. You can switch to a different Medigap plan or insurer during open enrollment, though switching may mean losing any discounts you had.

How Medigap Works Alongside Original Medicare

When you have both Original Medicare and a Medigap policy, the bills flow in a specific order. Medicare processes the claim first and pays its share. Your Medigap policy then receives the claim and pays the portion that Medicare did not cover, up to the limits of your plan.

You submit claims to Medicare as usual — your doctor or hospital does this for you in most cases. Once Medicare pays, the claim automatically goes to your Medigap insurer. You do not have to file a separate claim with Medigap; the two systems communicate directly. This means you typically see lower out-of-pocket costs than you would with Original Medicare alone, because Medigap covers the deductibles and coinsurance that Medicare leaves you responsible for.

Medigap does not cover everything. It does not pay for long-term care, dental work, vision care, hearing aids, or routine physicals. It also does not cover prescription drugs — you need a separate Part D prescription drug plan for that. Some Medigap plans cover some foreign travel emergencies, but coverage is limited.

Medigap Versus Medicare Advantage: The Key Differences

Medigap and Medicare Advantage are two different paths, and you must choose one or the other — you cannot have both at the same time. With Medigap, you keep Original Medicare and add a supplemental policy. With Medicare Advantage, you replace Original Medicare with a private plan that includes hospital, doctor, and usually prescription drug coverage in one package.

Medicare Advantage plans often have lower or zero premiums, but they come with network restrictions: you usually must see doctors in the plan's network, and you may need prior approval for certain services. Medigap has no network — you can see any doctor or hospital that accepts Medicare. Medicare Advantage plans include prescription drug coverage; Medigap does not. Medigap plans are standardized across the country; Medicare Advantage plans vary by region and insurer.

If you have Medigap and later want to switch to Medicare Advantage, you can do so during the annual Medicare open enrollment period (October 15 to December 7). If you have Medicare Advantage and want to switch to Medigap, you have 63 days from the date your Medicare Advantage plan ends. Missing this window means you may not be able to buy Medigap without paying a higher premium.

How to Compare Plans and Find the Right One for You

Start by deciding which plan letter makes sense for your budget and health needs. Plan A is the cheapest but covers the least. Plan G covers the most and is popular with people who want predictable costs. Plan N is a middle ground — it covers most costs but requires small copayments. Use the standardized coverage charts on Medicare.gov to see exactly what each plan covers.

Once you know which plan you want, get quotes from at least three insurers in your area. Premiums for the same plan can differ by hundreds of dollars per year between companies. You can get quotes by calling insurers directly, visiting their websites, or using the Medicare Plan Finder tool on Medicare.gov. Write down the monthly premium, any discounts for annual payment or automatic enrollment, and the insurer's customer service rating.

Check whether the insurer is financially stable and has a good reputation for paying claims. You can look up insurer ratings on the National Association of Insurance Commissioners (NAIC) website or ask your state's insurance commissioner's office. Once you choose a plan and insurer, you can enroll by phone, mail, or online, depending on the company's options.

Frequently Asked Questions

Can I switch Medigap plans or insurers after I buy one?

Yes, you can switch during the annual open enrollment period (October 15 to December 7) or during your state's Medigap open enrollment period if your state has one. Some states allow switching at any time. Outside these windows, the new insurer can deny you or charge more based on your health. Switching to a less comprehensive plan (like from G to A) may be easier than switching to a more comprehensive one.

Do I need a Medigap plan if I am still working and have employer health insurance?

Not necessarily. If your employer plan is primary and covers your costs well, you may not need Medigap. However, once you retire and lose that coverage, you will have a limited window to buy Medigap without penalties. Talk to your employer's benefits office about your options before you retire.

What happens to my Medigap coverage if I move to a different state?

Your Medigap policy remains valid in any state, but premiums may change because rates are set by state and region. Some insurers may not sell in your new state, so you may need to switch insurers. You can do this during the annual open enrollment period without penalty, even if you are switching to a different plan letter.

Does Medigap cover prescription drugs?

No. Medigap covers deductibles and coinsurance for hospital and doctor services, but not prescription drugs. You must enroll in a separate Medicare Part D prescription drug plan. You can buy Part D at the same time you buy Medigap, and you have the same open enrollment windows to avoid penalties.

Can I buy Medigap if I am under 65?

Generally, no. Medigap is designed for people on Medicare, which most people become may be able to access for at 65. Some people under 65 may have access to for Medicare due to disability or end-stage renal disease, and they can buy Medigap, but rules and availability vary by state. Contact your state's insurance commissioner's office to learn what options exist in your situation.