What Medicare Supplement Insurance Is and Why People Buy It

Medicare Supplement Insurance, also called Medigap, is a type of private insurance that works alongside Original Medicare (Part A and Part B). Original Medicare covers many healthcare costs, but it doesn't cover everything. When you receive medical services, Original Medicare typically pays its share, and you pay the rest out of your pocket. This remaining amount is called your "out-of-pocket cost." Medicare Supplement Insurance is designed to help pay some or all of these costs that Original Medicare leaves behind.

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According to 2023 data from the Centers for Medicare & Medicaid Services, over 11 million Medicare beneficiaries have some form of Medigap coverage. These individuals purchase these plans because they want predictability in their healthcare spending. Instead of facing unexpected medical bills, they pay a monthly premium to their insurance company and know in advance what their costs will likely be.

The main reasons people purchase Medicare Supplement Insurance include covering deductibles (the amount you pay before insurance kicks in), copayments (fixed amounts you pay per visit), and coinsurance (a percentage of costs you share with Medicare). For example, under Original Medicare Part B, you pay a $226 annual deductible in 2024, and then you typically pay 20% of approved amounts for most services. A Medicare Supplement plan can reduce or eliminate these payments.

It's important to understand that Medicare Supplement Insurance is different from Medicare Advantage (Part C). Medicare Advantage is an alternative to Original Medicare offered by private insurance companies, while Medigap works alongside Original Medicare. Medigap holders keep their Original Medicare coverage and add a supplement on top of it.

Practical Takeaway: Medicare Supplement Insurance exists to cover costs that Original Medicare doesn't pay. Understanding what gaps Medigap fills—such as deductibles, copayments, and coinsurance—helps you decide whether this type of coverage might reduce your healthcare expenses.

The Ten Standardized Medicare Supplement Plans

One of the most important things to know about Medicare Supplement Insurance is that the plans are standardized by the federal government. This means that Plan G offered by one insurance company must provide the exact same coverage as Plan G offered by another company. The government doesn't require you to use any particular insurance company—you can shop among different companies—but the benefits within each plan letter are identical across all insurers.

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Currently, there are ten different standardized Medicare Supplement plans, labeled A, B, C, D, F, G, K, L, M, and N. Each plan covers a different combination of healthcare costs. Plan A is the most basic, covering fewer costs than other plans. Plan G and Plan F (for those who became eligible before January 1, 2020) tend to be more comprehensive in terms of the number of costs covered. Plan N is a middle-ground option that covers many costs but includes some copayments for certain services.

Here's what all Medigap plans must cover: Part A coinsurance and hospital costs (up to an additional 365 days after Medicare coverage ends), Part B coinsurance or copayment, blood transfusions, and hospice coinsurance. Beyond these required coverages, different plans cover different combinations of other costs. For instance, Plan G covers Part B excess charges (amounts doctors charge above what Medicare approves), while Plan A does not. Plan K and Plan L are designed for people who want lower monthly premiums but are willing to pay more when they use healthcare services.

The ten plans are often grouped by how much they cover. "Comprehensive" plans cover most out-of-pocket costs, while basic plans leave more costs to you. Mid-level plans offer a balance between premium costs and out-of-pocket expenses. Because you can switch plans during certain times of the year, understanding the differences between plans helps you choose one that matches your expected healthcare use and budget.

Practical Takeaway: Knowing that plans A through N offer standardized coverage allows you to compare costs between insurance companies offering the same plan. You don't need to compare Plan G from Company X with Plan G from Company Y because their coverage is identical; you're mainly comparing premium prices.

How Medicare Supplement Insurance Pays Claims

When you have Medicare Supplement Insurance, the way healthcare costs are paid involves coordination between Medicare, your Medigap insurer, and you. Here's how the process typically works: You receive medical care, and a bill is submitted. Medicare processes the claim first and pays its share based on what it considers an approved amount. Your healthcare provider then sends information about what Medicare paid to your Medigap insurance company.

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The Medigap insurer reviews the claim and pays the portion that their plan is supposed to cover. For example, if you visit a doctor and the approved charge is $200, Medicare might pay $160 (80% of the approved amount after you've met your deductible), leaving $40 that you would normally owe. If your Medigap plan covers doctor visit copayments or coinsurance, the insurance company may pay that $40. In this case, you would pay nothing out of your pocket.

The time it takes for claims to process varies. Medicare typically processes claims within two weeks, and then your Medigap insurer processes their portion. In total, the process usually takes between two to four weeks, though some insurers process faster. You should receive an Explanation of Benefits (EOB) from Medicare showing what was paid, and a similar document from your Medigap insurer.

One important point: your healthcare provider cannot bill you for amounts that either Medicare or your Medigap plan should have paid, except for any out-of-pocket costs that are your responsibility under your specific plan. For instance, if your plan includes a copayment for a doctor visit, you pay that copayment. But if your plan should cover coinsurance and the provider bills you for it anyway, this is called "balance billing," which is generally not allowed.

It's worth noting that when you use services outside the United States, Medicare doesn't cover them, and most Medigap plans don't cover them either. However, some plans offer limited coverage for emergency services abroad. You should review your specific plan's coverage details for international care.

Practical Takeaway: Understanding the claim process helps you track your healthcare costs and know what to expect. Keep your EOB documents and compare them with bills from providers to catch errors.

Medicare Supplement Insurance Costs and Pricing Methods

Medicare Supplement Insurance requires you to pay a monthly premium to your insurance company. The premium you pay depends on several factors: which plan you choose (Plan A costs less than Plan G), which insurance company sells the plan, and your age and location. Unlike some insurance types, Medicare Supplement premiums cannot be based on your health status or medical history. Everyone with the same plan and age pays the same rate within the same insurance company and geographic area.

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Insurance companies use three main methods to set premiums for Medicare Supplement plans. The first method is called "community-rated" pricing. With community rating, all individuals the same age pay the same premium, regardless of when they purchased the plan. The second method is "issue-age-rated" pricing. With this method, your premium is based on your age when you first purchase the plan, and your rate increases as you get older. The third method is "attained-age-rated" pricing. With attained-age rating, your premium increases each year based on your current age, meaning you pay more each birthday.

In 2024, Plan A premiums range from approximately $120 to $200 per month depending on your location and insurance company. Plan G ranges from roughly $140 to $250 per month. Plan N typically costs $110 to $180 per month. These numbers vary considerably by state and insurer. For example, premiums in New York tend to be lower due to state regulations, while premiums in other states may be significantly higher. It's common for premiums to increase annually as healthcare costs rise and as you age.

When comparing costs between plans, you need to consider both your monthly premium and your expected out-of-pocket costs. A plan with a higher premium might have lower deductibles and copayments, resulting in lower overall costs if you use healthcare services frequently. Conversely, a plan with a lower premium might have higher out-of-pocket costs, making it better for people who rarely visit doctors. The best plan depends on your individual health situation and healthcare usage patterns.

Practical Takeaway: Request quotes from multiple insurance companies