Medicare Supplement Plans Fill the Gaps in Original Medicare

A Medicare Supplement plan (also called Medigap) is private insurance you buy to cover costs that Original Medicare does not pay. Original Medicare covers hospital stays, doctor visits, and some medical equipment, but leaves you responsible for deductibles, copayments, and coinsurance. A Medigap plan picks up some or all of those out-of-pocket costs.

Medigap is sold by private insurance companies, not by Medicare itself. You keep your Original Medicare coverage and pay a monthly premium to the insurance company on top of your Medicare Part B premium. The Medigap plan then pays its share of covered costs when you see a doctor or go to the hospital.

Medigap is different from Medicare Advantage (Part C), which is an alternative way to get Medicare coverage through a private plan. With Medigap, you use Original Medicare; with Advantage, you do not.

Key Takeaways

  • Medigap covers deductibles, copayments, and coinsurance that Original Medicare leaves you to pay, but does not cover dental, vision, hearing aids, or long-term care.
  • There are ten standardized Medigap plans (A through N), each with the same benefits no matter which insurance company sells it, though premiums vary by company and location.
  • You can enroll in Medigap during your initial enrollment period (the six months after you turn 65 and sign up for Medicare Part B), when insurers cannot deny you or charge more based on health history.
  • Outside the enrollment period, insurers can refuse to sell you Medigap or charge higher premiums based on your health, so timing matters.
  • Medigap premiums, deductibles, and coverage details change by plan letter and by insurance company, so comparing quotes from multiple insurers is necessary to find the lowest cost.

The Ten Standardized Medigap Plans and What Each Covers

Medicare sets the rules for what each Medigap plan must cover, so Plan A from one insurance company covers the same benefits as Plan A from another. The ten plans are labeled A, B, D, G, K, L, M, N, and two high-deductible versions of G and F (F is no longer sold to people new to Medicare). Each plan covers a different combination of costs.

Plan G is the most popular choice for new enrollees because it covers the Part B deductible (which is $240 in 2024, though this amount changes yearly) and most other out-of-pocket costs except the Part B excess charge (a charge some doctors add if they do not accept Medicare assignment). Plan N covers most costs but leaves you responsible for small copayments at the doctor and emergency room. Plans A, K, and L cover fewer costs and have lower premiums but leave you paying more when you use care.

The high-deductible versions of Plans G and F require you to pay a yearly deductible (around $2,700 in 2024) before the plan starts paying anything, but the monthly premium is much lower. These plans make sense only if you rarely see doctors or expect low medical costs in the coming year.

No Medigap plan covers dental, vision, hearing aids, prescription drugs, or long-term care. For prescription drugs, you need a separate Part D plan. For dental and vision, you either pay out of pocket or look into standalone dental and vision plans, which are not part of Medicare.

When You Can Enroll in Medigap Without Health Questions

Your Medigap enrollment period is the six-month window starting the month you turn 65 and sign up for Medicare Part B. During this period, insurance companies must sell you any Medigap plan you want and cannot ask about your health history, deny you coverage, or charge you more because of pre-existing conditions. This is called may provide issue rights.

If you enroll in Medigap during this six-month window, your coverage can start as early as the first day of the month you turn 65 (if you sign up for Part B that month) or the first day of the month after you sign up for Part B. Enrolling early means no gap in coverage between when Original Medicare starts and when Medigap begins.

If you miss this window, you can still buy Medigap later, but insurers can refuse to sell to you, charge you higher premiums based on your health, or impose a waiting period before covering pre-existing conditions. Some states have additional protections that extend may provide issue rights in certain situations (for example, if you were in a Medicare Advantage plan and it left your area), so check with your state insurance commissioner's office if you are outside the initial period.

How Medigap Premiums Work and What Affects the Cost

Medigap premiums vary widely by insurance company, by the plan you choose, by your age, and by where you live. The same Plan G might cost $120 a month with one insurer and $180 with another in the same city. Insurance companies use three main methods to set premiums: community-rated (everyone in your area pays the same regardless of age), age-rated (premiums rise as you age), and issue-age-rated (your premium is locked to your age when you enroll and stays lower as you age, but new enrollees pay more).

Your premium does not change based on how much medical care you use — Medigap is not like health insurance where claims history affects your rate. However, insurers can and do raise premiums across an entire plan or company to keep up with medical inflation and claims costs. These increases affect everyone on that plan, not just you.

To find the lowest premium, you need to get quotes from multiple insurers. Medicare publishes a list of Medigap insurers in your state on Medicare.gov, and many state health insurance information programs (SHIPs) offer free help comparing plans and costs. Switching to a cheaper plan from a different company is possible, though you may face health underwriting if you switch outside your initial enrollment period.

How Medigap Works When You See a Doctor or Go to the Hospital

When you receive care, Original Medicare pays its share first, then your Medigap plan pays its share according to the plan you chose. You typically pay nothing out of pocket if your plan covers that cost, though some plans (like Plan N) have small copayments.

For example, if you see a doctor who accepts Medicare assignment and your plan is Plan G, Original Medicare pays 80 percent of the approved amount after you meet the deductible, and Plan G pays the remaining 20 percent coinsurance. You pay nothing. If you choose Plan N instead, you pay a small copayment (around $20 for a doctor visit) and Plan N covers the rest.

Medigap does not work with out-of-network doctors or facilities. If you see a doctor who does not accept Medicare, neither Original Medicare nor your Medigap plan will pay, and you pay the full bill. This is why staying in-network matters even with Medigap coverage.

Medigap vs. Medicare Advantage: Which Route to Choose

Medicare Advantage (Part C) is an alternative to Original Medicare plus Medigap. With Advantage, you get hospital, doctor, and usually prescription drug coverage all in one plan from a private insurer, often with no monthly premium beyond your Part B premium. However, Advantage plans have networks, copayments, prior authorization requirements, and annual out-of-pocket limits.

Medigap works best if you want to see any doctor who accepts Medicare without asking permission first, if you travel frequently, or if you want predictable costs (no surprise bills if you go out of network). Advantage works best if you want lower or no monthly premiums, if you use a lot of prescription drugs (Advantage includes Part D), or if you are comfortable with networks and prior authorization.

You cannot have both Medigap and Advantage at the same time. If you have Medigap and later switch to Advantage, you can usually switch back to Medigap during the annual open enrollment period (October 15 to December 7), though you may face health underwriting if you have been off Medigap for a while.

Common Mistakes to Avoid When Choosing Medigap

The biggest mistake is waiting to enroll in Medigap after your initial six-month window closes. Once that window ends, you lose may provide issue rights and insurers can deny you or charge much higher premiums. If you are turning 65 and signing up for Medicare, enroll in Medigap during the same month or the month after you sign up for Part B.

Another common error is choosing a plan based on premium alone without checking what it covers. Plan A has the lowest premium but leaves you paying more out of pocket for deductibles and coinsurance. Plan G costs more monthly but covers the Part B deductible, which saves money if you see doctors regularly. Calculate your likely costs under each plan, not just the premium.

A third mistake is not comparing quotes from multiple insurers. Premiums for the same plan vary significantly by company, and shopping around can save hundreds of dollars a year. Use Medicare.gov's plan finder or contact your state SHIP for free help comparing options.

Finally, do not assume your current health insurance will convert to Medigap automatically. When you turn 65 and enroll in Medicare, your employer or individual health plan ends. You must actively choose and enroll in Medigap (or Advantage) during your enrollment period.

Frequently Asked Questions

Can I switch Medigap plans after I enroll?

Yes, you can switch to a different Medigap plan from the same or a different company at any time. However, if you switch outside your initial enrollment period, the new insurer can deny you, charge higher premiums, or impose waiting periods for pre-existing conditions. Switching during the annual open enrollment period (October 15 to December 7) does not may provide better terms, so check with the new insurer first.

Does Medigap cover prescription drugs?

No. Medigap covers hospital and doctor costs, but not prescription medications. You need a separate Medicare Part D prescription drug plan. You can enroll in Part D when you first sign up for Medicare or during the annual open enrollment period, though waiting to enroll can result in a permanent penalty on your premium.

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

Your Medigap plan may not be available in your new state because insurers do not sell all plans in all states. You will likely need to switch to a plan that is sold in your new state. Contact your current insurer or your new state's SHIP to find out what plans are available and how to switch without losing coverage.

Do I need Medigap if I have retiree health insurance from my former employer?

Not necessarily. If your employer plan is creditable (covers at least as much as Medicare), you may not need Medigap. However, if your employer plan ends or you lose coverage, you can enroll in Medigap during a special enrollment period without health underwriting. Check your employer plan documents or contact your benefits administrator to understand your coverage.

What is the difference between Medigap Plan F and Plan G?

Plan F (no longer sold to people new to Medicare after 2020) covered the Part B deductible and excess charges. Plan G covers the Part B deductible but not excess charges. For new enrollees, Plan G is the closest alternative to Plan F and is the most popular choice. Both cover most out-of-pocket costs, but Plan G premiums are typically lower.