Medicare Supplement Insurance Fills the Gaps Medicare Leaves Behind

Medicare covers a lot, but not everything. When you go to the hospital or see a doctor, you still owe deductibles, copayments, and coinsurance. Medicare Supplement insurance — also called Medigap — is a private insurance policy that pays some or all of those out-of-pocket costs. It does not replace Medicare; it works alongside it. Medicare pays first, then your supplement policy pays what Medicare does not cover.

You buy Medigap from a private insurance company, not from Medicare or the government. The monthly premium comes out of your pocket, separate from your Medicare Part B premium. The amount you pay depends on which plan you choose, your age, where you live, and which insurance company sells it. Plans are standardized by the federal government — a Plan G from one company covers the same things as Plan G from another — but prices vary significantly between insurers.

Key Takeaways

  • Medicare Supplement insurance is sold by private companies and pays deductibles, copayments, and coinsurance that Medicare does not cover.
  • Plans are labeled A through N, and each letter represents a fixed set of benefits — the same across all insurers, though prices differ.
  • You can enroll during your initial Medicare enrollment period or during the annual open enrollment period, though some states allow year-round enrollment.
  • The best time to buy is within six months of turning 65 or enrolling in Medicare Part B, because insurers cannot deny you or charge more based on health history during that window.
  • You must have Medicare Part A and Part B to buy a Medigap policy; it does not work with Medicare Advantage plans.

The Ten Standardized Plans and What Each One Covers

The federal government defines ten Medigap plans, labeled A through N. Each plan covers a different combination of costs. Plan A is the most basic and least expensive; Plan G and Plan N are the most comprehensive and most expensive. All plans cover the Part A deductible (the amount you owe before Medicare hospital coverage kicks in), but they differ on whether they cover the Part B deductible, how much coinsurance you owe for hospital stays, and whether they cover foreign travel emergencies.

Plan G is the most popular choice for people newly turning 65, because it covers nearly everything except the Part B deductible (which is $240 in 2024, though this amount changes yearly). Plan N is less expensive than Plan G but requires you to pay a small copayment at the doctor's office and a higher coinsurance amount for hospital stays. Plan A costs less but covers fewer things. The right plan depends on how much you expect to use healthcare and how much monthly premium you can afford.

You can view a detailed comparison table on the Medicare.gov website showing exactly what each plan covers. Because the benefits are standardized, the only reason to choose one company over another is price. You should get quotes from at least three insurers before enrolling.

When You Can Enroll and How to Lock in the Best Rates

The best time to buy Medigap is during your initial enrollment period, which lasts six months from the month you turn 65 or the month you enroll in Medicare Part B, whichever comes later. During this window, insurance companies cannot refuse to sell you a policy, cannot charge you more because of health problems, and cannot exclude any conditions you already have. This is called may provide issue protection.

If you miss this window, you can still buy Medigap during the annual open enrollment period, which runs from October 15 to December 7 each year. Coverage starts January 1. However, outside your initial enrollment period, insurers can deny you, charge you more, or exclude pre-existing conditions — depending on your state's rules. Some states offer additional enrollment windows or protections, so check with your state insurance commissioner's office.

Once you enroll, your coverage continues as long as you pay the premium. You can switch to a different plan or a different company during the annual open enrollment period, though switching may trigger medical underwriting if you move to a more comprehensive plan.

How Medicare Supplement Works With Your Other Coverage

Medigap works only with Original Medicare (Part A and Part B). If you have a Medicare Advantage plan instead, you cannot buy a Medigap policy — Medicare Advantage already includes out-of-pocket cost limits, so Medigap would be redundant and is not legally sold to Advantage enrollees. If you have both Medigap and Advantage coverage, the Medigap policy will not pay anything.

If you have retiree health insurance from a former employer, you may not need Medigap, or you may want a less comprehensive plan. Check your retiree plan documents to see what it covers before buying a supplement. Some employers' plans coordinate with Medicare and cover costs that Medigap would cover; others do not. Your former employer's benefits office can tell you whether Medigap makes sense for you.

Medigap does not cover prescription drugs. You need a separate Part D prescription drug plan for that, which you can enroll in during the same annual open enrollment period.

What Medigap Does Not Cover

Medigap covers the gaps in Original Medicare, but it does not cover everything. It does not pay for long-term care (nursing home or in-home care), dental work, vision care, hearing aids, or routine physical exams. It does not cover services Medicare does not cover, such as cosmetic surgery or experimental treatments. If Medicare says no, Medigap says no too.

Some plans cover a small amount of foreign travel emergency care if you are outside the United States, but coverage is limited and does not explore to routine care abroad. If you travel internationally regularly, ask your insurer about the details before you go.

How to Compare Plans and Get Quotes

Start by deciding which plan letter makes sense for your situation. If you want the broadest coverage and can afford the premium, Plan G is the standard choice. If you want to save money and do not mind small copayments, Plan N is worth comparing. If you are on a tight budget, Plan A or Plan C may be your only option, though they cover less.

Once you have chosen a plan letter, get quotes from at least three insurers. You can call insurers directly, use the Medicare Plan Finder tool on Medicare.gov, or contact your State Health Insurance information Program (SHIP), which offers free counseling. SHIP can also tell you about any state-specific rules or programs that might affect your choice. Prices vary widely — the same plan can cost $100 a month from one company and $180 from another — so shopping is worth the time.

When you get a quote, confirm the plan letter, the monthly premium, and whether the company offers any discounts (some offer discounts for paying by automatic bank transfer or for being a long-time customer). Ask whether the premium is may provide not to increase for a set period, though most companies do not offer such guarantees.

What Happens to Your Premium Over Time

Medigap premiums increase over time. Most companies use age-based rating, which means your premium goes up as you get older. Some use issue-age rating, which means your premium is based on your age when you enroll and does not increase as you age (though it may increase for other reasons, such as inflation). A few use community rating, which means everyone in your state pays the same premium regardless of age.

All companies can raise premiums for inflation or because their costs have gone up, but they cannot single you out for a rate increase because you filed claims. Rates are approved by your state insurance commissioner before they take effect. If your premium increases significantly, you can switch to a different plan or company during the annual open enrollment period without medical underwriting.

Frequently Asked Questions

Can I buy Medigap if I have a pre-existing condition?

Yes, during your initial six-month enrollment period after turning 65 or enrolling in Medicare Part B. Insurers cannot deny you or charge more. Outside that window, rules depend on your state — some states may provide issue regardless of health, while others allow insurers to deny you or exclude conditions. Check with your state insurance commissioner's office.

What is the difference between Medigap and Medicare Advantage?

Medicare Advantage is an alternative to Original Medicare sold by private insurers; it includes hospital, doctor, and usually prescription drug coverage all in one plan. Medigap is a supplement to Original Medicare that only pays out-of-pocket costs. You choose one or the other, not both. Advantage plans have networks and referrals; Medigap works with any doctor who accepts Medicare.

Do I have to enroll in Medigap when I turn 65?

No, but waiting can cost you. If you enroll after your initial six-month window, insurers can deny you, charge more, or exclude pre-existing conditions — depending on your state. If you are healthy and do not expect to use much healthcare, you might skip Medigap, but you lose may provide issue protection if you change your mind later.

Can I switch Medigap plans or companies?

Yes, during the annual open enrollment period (October 15 to December 7). If you switch to a less comprehensive plan, you usually do not need medical underwriting. If you switch to a more comprehensive plan, the new company may require medical underwriting. Some states allow switching year-round without underwriting.

Does Medigap cover prescription drugs?

No. You need a separate Medicare Part D prescription drug plan. You can enroll in Part D during the same annual open enrollment period as Medigap, or during your initial enrollment period when you turn 65. If you do not enroll in Part D when you are first may be able to access, you may owe a penalty if you enroll later.