Filling the original Medicare gap: What is Medicare supplement insurance?

If you’ve read even just a little about Medicare, you may have already come across the synonymous terms Medicare supplement insurance and Medigap. Supplement insurance is optional, and it’s relevant only for the roughly half of all Medicare recipients who enroll in original Medicare, which is administered by the federal government.

Medicare Advantage plans are offered by insurance companies who build supplemental coverage into the all-in-one policies they market, so an additional policy isn’t needed. In fact, if you select Medicare Advantage, insurance companies aren’t allowed to sell you a Medigap policy.

For many Medicare beneficiaries, supplemental coverage is essential because original Medicare doesn’t cover all their health care expenses. An additional Medigap policy can help fill those gaps, though at the cost of an additional premium. As of 2025, new Medicare cost figures and plan rules shape how Medigap fits into the picture (more on this below).

Health care gaps Medigap coverage can help fill

Original Medicare covers a wide range of health-related services and medical supplies for its beneficiaries. But there are some costs, such as copayments and deductibles, that can result in substantial out-of-pocket expenses. Medigap can pick up all or most of the out-of-pocket costs that you’d have to pay if all you had was the hospital and medical insurance provided by parts A and B of original Medicare.

These Medigap plans are operated and marketed by insurance companies, not the federal Medicare program, although the federal government is responsible for establishing the guidelines that insurance companies must follow.

Some Medigap policies pay for emergency health care received abroad, as original Medicare doesn’t cover medical bills incurred outside the U.S. If foreign travel health coverage matters to you, make sure any Medigap policy you purchase includes it.

Four out of five (80%) adults enrolled in original Medicare are also enrolled in some type of supplemental policy, according to KFF, the health policy organization formerly known as the Kaiser Family Foundation. Further, more than half receive supplemental coverage through employer-sponsored retiree health plans, union plans, or even Medicaid, the government program that provides health coverage for low-income people.

Some employers and unions are willing to purchase Medigap policies for their employees and retirees. But even if you have to purchase your own policy, it’s worth considering.

Important things to know about Medigap policies

• Spouses require separate policies. Like original Medicare, a Medigap policy only covers one person, so each Medicare beneficiary in your household needs an individual policy.
• Comparison shopping pays. You might find identical coverage from another insurance company that costs hundreds of dollars less annually. Premiums can increase as you age. Some states limit Medigap premium costs.
• Renewals are guaranteed. Any standardized Medigap policy is required to offer you a renewal, even if you develop health problems while on the policy. The company can’t cancel you as long as you continue to make premium payments.
• Drug coverage is separate. As of January 6, 2006, Medigap policies stopped covering prescription medications, but you can enroll in Medicare Part D for prescription drug coverage.
• Additional coverage may be needed. A Medigap plan won’t cover long-term care, dental, or vision care. You may want to explore separate insurance options for these services.

Understanding the different Medigap plans (A through N)

If you think understanding parts A, B, C, and D—the basic building blocks of the Medicare program—is a bit of a challenge, the variety of Medigap plans can be equally confusing. In all but three states (Wisconsin, Massachusetts, and Minnesota), insurance companies can only sell a standardized Medigap policy identified by letters A through N (although some letters have been discontinued and others are closed to new enrollees). Unlike Medicare parts, which cover different types of care, Medigap plans help cover certain out-of-pocket costs not included in original Medicare.

Each of the lettered plans offers a different set of benefits, and the costs vary with the amount of coverage. In general, Plan A provides the fewest benefits and has the lowest premiums. Medigap plans that more effectively fill in cost gaps, such as plans F or G, usually have a higher premium. Here’s a rundown:

• Plans A, B, D, G, K, L, M, and N. Still active and open to new enrollees (in most states). There’s also a high-deductible version of G.
• Plans C and F. Closed to new enrollees since January 1, 2020 (but existing policyholders can keep them). For existing Plan F enrollees, there’s also a high-deductible version available.
• Plans E, H, I, and J. Phased out back in 2010 and no longer available.

Federal guidelines require that each Medigap plan run by an insurance company must offer the same basic benefits, no matter which insurance company sells it. So Plan G offered by one insurer provides the same benefits as Plan G offered by another. The prices may differ, but the benefits won’t.

According to the American Association for Medicare Supplement Insurance, the majority of new Medicare enrollees since 2020 have chosen Plan G, which covers nearly all costs except the Part B deductible.

Consider the premium cost to ensure it fits within your budget before choosing a plan.

The bottom line

Whether you get it for free, at a discount from an employer or a union, or pay for it out of your own pocket, some form of supplemental insurance is recommended for enrollees of original Medicare. If you have no choice but to pay for your own Medigap policy, start by finding a list of supplemental plans offered in your area using the Medigap plan finder.

Your best chance to buy without medical underwriting is during your one-time, six-month Medigap open enrollment period, which begins when you first enroll in Part B. The annual Medicare Open Enrollment window each fall (October 15 to December 7) is when you can make other changes, such as switching between original Medicare and Medicare Advantage.

References

• What’s Medicare Supplement Insurance (Medigap)? | medicare.gov
• Medigap Costs | medicare.gov
• Find a Medigap Policy That Works for You | medicare.gov
• A Snapshot of Sources of Coverage Among Medicare Beneficiaries | kff.org
• Medicare Insurance Data Statistics 2024 | medicaresupp.org