What a Medicare Supplement Plan Does and Why You Might Need One

A Medicare Supplement plan (also called Medigap) is insurance you buy from a private company to cover costs that Original Medicare leaves you paying yourself — copayments, coinsurance, and deductibles. Original Medicare covers a lot, but not everything. If you go to the hospital, you pay a deductible. If you see a specialist, you pay 20 percent of the cost. A supplement plan fills those gaps so you know in advance what your out-of-pocket costs will be.

You do not have to buy a supplement plan. Some people choose a Medicare Advantage plan instead, which is a different type of coverage run by private insurers. Others stay on Original Medicare alone and pay out-of-pocket when costs come up. But if you want predictable costs and the freedom to see any doctor who takes Medicare, a supplement plan is the most straightforward choice.

Key Takeaways

  • Medicare Supplement plans are standardized by the federal government, so Plan G from one company covers the same things as Plan G from another — only the price differs.
  • Plan G and Plan N are the most common choices for people newly may be able to access for Medicare, and Plan G covers more but costs more.
  • You have a six-month window starting the month you turn 65 and enroll in Medicare Part B to buy a supplement plan without being asked health questions.
  • Outside that window, insurers can deny you or charge more based on your health history, so timing your purchase matters.
  • Comparing plans means comparing price quotes from multiple insurers for the same plan letter, not comparing different plan letters to each other.

The Ten Standardized Plans and What They Cover

The federal government defines ten Medicare Supplement plans, labeled A through N. Each plan letter covers a fixed set of costs. Plan A is the most basic and cheapest. Plan G covers more and costs more. Plan N is in the middle. The exact same Plan G from Company X covers identical costs as Plan G from Company Y — the only difference is price.

Plan G is currently the most popular choice because it covers most of what Original Medicare does not, including the Part B deductible (the amount you pay before Medicare starts paying). Plan N is less expensive but requires you to pay a copayment when you see a doctor and a higher copayment for emergency room visits. Plan A is the cheapest but leaves you responsible for the Part B deductible, which changes yearly and was $240 in 2024.

You do not need to understand all ten plans. Start by asking yourself: do you want the lowest monthly premium, or do you want the lowest out-of-pocket costs when you actually use care? If you want predictable costs and rarely skip doctor visits, Plan G usually makes sense. If you want the lowest monthly payment and are willing to pay per visit, Plan N might fit better.

When You Can Buy Without Health Questions

The six-month open enrollment window is the single most important date in supplement shopping. It starts the first day of the month you turn 65, as long as you enroll in Medicare Part B that same month. It lasts six months. During this window, any insurance company must sell you any supplement plan at the same price they charge everyone else your age — they cannot ask about your health, deny you, or charge you more because you have diabetes or heart disease.

If you miss this window, you enter what is called may provide issue rights in only specific situations: if you lose employer coverage, if you move out of an insurer's service area, or if your Medicare Advantage plan closes. Outside those situations and outside the open enrollment window, insurers can refuse to sell you a plan or charge you significantly more. Some people are denied coverage entirely.

If you are already on Medicare and did not buy a supplement plan when you first enrolled, you can still buy one, but you will likely face health questions. The cost difference between buying during the open window and buying years later can be hundreds of dollars per year.

How to Compare Plans and Get Price Quotes

Comparing supplement plans means getting quotes for the same plan letter from multiple insurers. Do not compare Plan G to Plan N — that is comparing different coverage. Instead, get the price for Plan G from five different companies, then decide if the extra coverage is worth the price difference compared to Plan N from those same companies.

You can get quotes by calling insurers directly, visiting their websites, or using the Medicare Plan Finder tool on Medicare.gov. The Plan Finder tool lets you enter your zip code and see which plans are available in your area and their monthly premiums. Prices vary by location and by age, so a quote for someone in Ohio will not match a quote for someone in Florida.

When you get a quote, confirm three things: the plan letter, the monthly premium, and whether the price is locked in or will increase. Some insurers raise prices every year. Others use community rating, which means everyone in your state pays the same price regardless of age. A few use issue-age rating, which means your price is set based on your age when you buy and stays the same as you get older — but other people who buy at older ages pay more.

Timing Your Purchase Around Your 65th Birthday

If you are turning 65 soon, enroll in Medicare Part B in the three months before your birthday month or during your birthday month itself. Then, during that same month or within the next six months, contact supplement insurers and buy a plan. You do not have to buy when ready — you have the full six months — but the sooner you buy, the sooner your coverage starts and the sooner you stop paying out-of-pocket costs.

If you are already on Medicare and did not buy a supplement plan, you can still buy one at any time, but you will face health underwriting. Some insurers will still sell to you; others will not. Call insurers in your state and ask whether they are currently accepting applications from people outside the open enrollment window. Prices will be higher than they would have been during your window.

What to Ask Your Doctor and Insurance Company

Before you choose between Plan G and Plan N, ask your primary care doctor how often you typically see specialists and whether you use urgent care or emergency services. If you see a cardiologist and an endocrinologist regularly, the copayments in Plan N add up. If you rarely go to the doctor, Plan N's lower premium might make more sense.

Once you have narrowed your choice to one or two plan letters, call the insurance companies and ask: Is this price locked in, or will it increase? Do you use community rating or issue-age rating? What is your process if I need to file a claim? Can I see any doctor who takes Medicare, or do I need to use a network? (The answer should be any doctor — that is the point of a supplement plan.)

What Happens After You Buy a Plan

Once you buy a supplement plan, the insurance company sends you a policy document and a member ID card. You show the card to your doctor's office along with your Medicare card. The doctor's office bills Medicare first, then automatically bills your supplement plan for the costs Medicare does not cover. You should receive an explanation of benefits from both Medicare and your supplement insurer after each visit.

You can switch to a different supplement plan once per year during the annual enrollment period, which runs from October 15 to December 7. If you switch, your new coverage starts January 1. You do not need a reason to switch — you can change plans straightforward because you found a better price or want different coverage. However, if you switch to a plan with less coverage, you may face health questions from the new insurer, so switching to more coverage is safer.

Frequently Asked Questions

Can I use a supplement plan with a Medicare Advantage plan?

No. A supplement plan is designed to work with Original Medicare. If you have a Medicare Advantage plan, you cannot buy a supplement. If you want to switch from Medicare Advantage to Original Medicare plus a supplement, you can do so during the annual enrollment period, but you will need to buy a supplement plan at that time and may face health questions if you are outside your initial open enrollment window.

What if I move to a different state?

Supplement plans are regulated by state, so your plan may not be available in your new state. Contact your current insurer and ask whether they operate in your new state. If they do not, you will need to buy a new plan from an insurer that does. Because you are losing coverage due to a move, you have may provide issue rights and cannot be denied or charged more based on health.

Do supplement plans cover prescription drugs?

No. Supplement plans cover only the costs that Original Medicare leaves unpaid. Prescription drug coverage is separate and is called Part D. You buy Part D from a private insurer during the same enrollment periods as your supplement plan. You can have both a supplement plan and a Part D plan at the same time.

What if my supplement plan increases its price too much?

You can switch to a different plan or a different insurer during the annual enrollment period each October through December. You do not need permission or a reason. However, if you switch to a plan with less coverage, the new insurer may ask health questions. Switching to the same plan letter from a cheaper insurer, or to more coverage, is safer.

Can I buy a supplement plan before I turn 65?

No. You must be enrolled in Medicare Part A and Part B before you can buy a supplement plan. You can enroll in Medicare starting three months before the month you turn 65. Once you are enrolled in Part B, your six-month open enrollment window for supplement plans begins.