Medicare Supplemental Insurance Fills the Gaps That Original Medicare Leaves

Medicare Supplemental Insurance, also called Medigap, is a private insurance policy you buy to cover costs that Original Medicare (Parts A and B) does not pay. Original Medicare covers a large share of hospital and doctor bills, but leaves you responsible for deductibles, copayments, and coinsurance. Medigap policies are sold by private insurers and designed to pay some or all of those out-of-pocket costs.

You do not need Medigap if you have Medicare Advantage (Part C) instead of Original Medicare — those plans include their own out-of-pocket limits and do not work with Medigap policies. But if you stay on Original Medicare, Medigap can reduce the amount you pay when you see a doctor, go to the hospital, or need other covered services.

Key Takeaways

  • Medigap policies cover deductibles, copayments, and coinsurance that Original Medicare does not pay, but they do not cover services Medicare itself does not cover.
  • There are ten standardized Medigap plans (A through N), each covering a different combination of costs; the plan letter tells you what is covered, not the insurance company.
  • You can enroll in Medigap during your initial Medicare enrollment period or during the Medigap open enrollment period, when insurers cannot deny you or charge more based on health history.
  • Medigap premiums vary by insurer, age, and location, and some plans cost significantly more than others even though they cover the same benefits.
  • If you miss the enrollment windows, you may face higher premiums or denial of coverage, so timing matters.

The Ten Standardized Medigap Plans and What Each Covers

All Medigap policies are standardized by federal law, which means Plan A from one insurance company covers exactly 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. The letter tells you which costs are covered; the insurance company name does not change the coverage.

Plan G and Plan N are the most common choices today because they offer broad coverage at a middle price point. Plan G covers your Part B coinsurance (the 20% of doctor bills you normally pay after Medicare pays 80%), your hospital coinsurance, and your Part B deductible. Plan N covers most of the same but charges you a small copayment at the doctor's office and for emergency room visits.

Plans A, B, D, K, and L cover fewer costs and have lower premiums. Plan A is the most basic and cheapest. Plans K and L include annual out-of-pocket limits, meaning once you hit that limit, the plan covers 100% of remaining costs for the rest of the year. The high-deductible versions of Plans G and F require you to pay a large annual deductible (the amount changes each year) before the plan starts paying anything, but the monthly premiums are much lower.

You can compare what each plan covers using the official Medicare Medigap comparison chart on Medicare.gov, which shows side-by-side which costs each plan pays.

When You Can Enroll in Medigap and Why Timing Matters

The best time to enroll in Medigap is during your initial Medicare enrollment period, which is the six-month window that starts the month you turn 65 and enroll in Original Medicare Part B. During this window, insurers cannot deny you coverage or charge you more because of health problems — a protection called may provide issue.

If you miss that window, you can still enroll during the Medigap open enrollment period, which runs for six months starting the first day of the month you turn 65 and enroll in Part B. After that period ends, you lose may provide issue protection. Insurers can then deny you coverage, charge you higher premiums based on your health history, or impose waiting periods for pre-existing conditions. Some states offer additional windows, but they vary.

If you have Medicare Advantage and later switch to Original Medicare, you may have a second chance at may provide issue Medigap enrollment. This window is usually 63 days from the date you disenroll from Medicare Advantage. Check with your state insurance commissioner's office to confirm the exact rules in your state.

How Medigap Premiums Are Set and What You Will Pay

Medigap premiums vary widely by insurance company, your age, your location, and the plan you choose. The same Plan G can cost $100 a month from one insurer and $200 a month from another in the same city. There is no single "correct" price — you have to shop and compare.

Insurers use three main methods to set premiums. Community-rated plans charge everyone in your area the same price regardless of age. Age-rated plans charge more as you get older. Issue-age-rated plans base your premium on your age when you first enroll, and then increase it over time, but you never pay as much as someone who enrolls at an older age. Most insurers use age-rated or issue-age-rated pricing.

Premiums also increase over time due to inflation and rising healthcare costs. Some insurers raise rates more steeply than others. Before you enroll, ask the insurer how they have raised rates in the past and what they project for the future. You can also switch to a different Medigap plan or insurer during the annual open enrollment period (October 15 to December 7), though you may face medical underwriting if you switch to a plan with richer benefits.

What Medigap Does Not Cover

Medigap only covers costs that Original Medicare itself covers. It does not pay for services Medicare does not cover, such as dental work, vision exams, hearing aids, or long-term care. If you need those services, you will have to pay out of pocket or buy separate coverage.

Medigap also does not cover prescription drugs. If you take medications, you need to enroll in a separate Medicare Part D prescription drug plan. You can enroll in Part D at the same time you enroll in Original Medicare and Medigap, or during the annual open enrollment period.

Medigap does not work with Medicare Advantage. If you have a Medicare Advantage plan, you cannot use a Medigap policy. Medicare Advantage plans include their own out-of-pocket limits and usually cover prescription drugs, but they often have narrower networks of doctors and hospitals.

How to Compare and Choose a Medigap Plan

Start by deciding which plan letter fits your needs and budget. If you see many doctors or expect high medical costs, Plan G or Plan N offer broad coverage. If you are healthy and want to minimize monthly premiums, Plan A or a high-deductible plan may be cheaper overall. Use the official Medicare Medigap comparison tool at Medicare.gov to see what each plan covers.

Once you have chosen a plan letter, get quotes from at least three insurers in your area. You can call insurers directly, use Medicare.gov's plan finder, or contact your state health insurance counseling program (often called SHIP or HICAP). Comparing quotes takes time but can save you hundreds of dollars a year.

Ask each insurer about their customer service ratings, how they handle claims, and whether they have raised rates significantly in recent years. A slightly cheaper premium today may not be worth it if the company has a history of steep rate increases or poor service.

Medigap Enrollment and What Documents You Need

To enroll in Medigap, contact the insurance company directly by phone, mail, or online. You will need your Medicare card, your Social Security number, and information about any current health coverage. Most insurers do not require a medical exam or health questionnaire if you enroll during your may provide issue period.

Your coverage usually starts on the first day of the month after the insurer receives your process and payment. Some insurers offer faster processing if you explore online. Keep copies of your enrollment confirmation and your policy documents for your records.

If you enroll outside the may provide issue period, the insurer may ask detailed health questions and may take weeks or months to make a decision. Some may deny you or impose waiting periods. This is another reason to enroll during one of the protected windows if at all possible.

Frequently Asked Questions

Can I switch Medigap plans or insurers after I enroll?

Yes, you can switch during the annual open enrollment period (October 15 to December 7) without medical underwriting if you stay on the same plan letter or switch to Plan A, B, D, K, L, or M. If you switch to a richer plan like Plan G or N, the new insurer may ask health questions and can deny you or charge more. Some states allow switching at other times under certain conditions.

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

Your current Medigap policy may not be available in your new state because insurers do not operate everywhere. Contact your current insurer to ask if they cover your new state. If not, you will need to enroll in a new policy in your new state. Depending on your situation, you may have may provide issue protection or may face medical underwriting.

Do I need Medigap 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. But once you retire and lose that coverage, you will want to enroll in Medigap during your may provide issue period. Talk to your employer's benefits office about your options before you retire.

Will Medigap cover me if I travel outside the United States?

Original Medicare does not cover care outside the U.S., so Medigap does not either. If you travel internationally, you will need to buy separate travel health insurance. Some Medigap plans offer limited coverage for emergency care in Canada and Mexico, but check your policy details.

What is the difference between Medigap and Medicare Advantage?

Medigap works with Original Medicare and covers out-of-pocket costs. Medicare Advantage is an alternative to Original Medicare sold by private insurers and includes its own doctor networks, out-of-pocket limits, and usually prescription drug coverage. You cannot have both at the same time. Medicare Advantage often costs less in premiums but may have higher copayments and narrower provider choices.