A Medicare Supplement Plan Pays Some of the Costs That Original Medicare Doesn't Cover

Original Medicare covers a lot, but it leaves gaps. You still owe a deductible before coverage starts, you pay 20% of the cost of doctor visits and tests, and you pay the full cost of most dental and vision care. A Medicare Supplement plan (also called Medigap) is insurance you buy from a private company to cover some or all of those gaps. It works alongside Original Medicare — it does not replace it.

When you see a doctor, Original Medicare pays its share first. Then your Medigap plan pays what it is supposed to cover under the plan you chose. You send in the claim, or your doctor's office does it for you. The timing matters: you can only buy a Medigap plan during certain windows, and the price depends on your age and health when you first sign up.

Key Takeaways

  • Medicare Supplement plans cover costs that Original Medicare leaves unpaid, such as deductibles, coinsurance, and copays.
  • There are 10 standardized Medigap plans (A through N), and each one covers a different set of gaps — you choose which plan fits your needs and budget.
  • You must have Original Medicare Part A and Part B to buy a Medigap plan; you cannot use it with Medicare Advantage.
  • The best time to buy is during your initial enrollment window, when insurers cannot charge more based on your health history.
  • Medigap plans are sold by private insurance companies, not Medicare, and premiums vary by company, location, and age.

The 10 Standardized Medigap Plans and What Each One Covers

Medicare sets the rules for what each Medigap plan must cover, so Plan A from one company covers the same things as Plan A from another company. The difference is price. The 10 plans are labeled A, B, D, G, K, L, M, N, and two high-deductible versions of G and F. Most people choose from Plans A, G, or N because they balance cost and coverage.

Plan A is the most basic and usually the cheapest. It covers the Part B deductible, coinsurance, and copays, but not the Part A deductible. Plan G covers more — it pays the Part A deductible and most of what Plan A covers, but you pay a higher monthly premium. Plan N is middle ground: it covers many gaps but leaves you paying small copays at the doctor's office and for emergency room visits.

The high-deductible versions of Plans F and G cost much less per month, but you pay a yearly deductible (around $2,700 in 2024, though this amount changes yearly) before the plan pays anything. These work well for people who are healthy and do not expect many doctor visits. You can compare the plans side by side on Medicare.gov, or ask your doctor's office which plan their billing staff sees most often — that can tell you which one causes the fewest headaches in practice.

When You Can Buy a Medigap Plan and Why Timing Matters

The best time to buy is your initial enrollment window, which is the six months after you turn 65 and sign up for Medicare Part B. During this window, insurance companies cannot turn you down or charge you more because of health problems you already have. After this window closes, you can still buy a plan, but the company can charge more if you have diabetes, heart disease, or other conditions.

Some states have different rules and allow you to buy without health questions at other times, but most do not. If you miss the window and want to switch plans later, you may face a waiting period or be denied coverage for pre-existing conditions. A few life events — like moving to a new state or losing other insurance — can reopen your window, but you have to act within 60 days.

If you are still working and have health insurance through your job, you can delay buying Medigap without penalty, as long as you sign up within 63 days of losing that coverage. Keep records of when your work insurance ended, because you will need to prove it.

How Much Medigap Plans Cost and What Affects the Price

Premiums vary widely depending on where you live, which company you choose, and how old you are. A Plan A might cost $100 a month in one state and $180 in another. The same plan from the same company might cost $120 at age 65 and $200 at age 75. There is no single "right" price — you have to get quotes from multiple companies to compare.

Insurance companies use three different pricing methods: age-attained (your premium goes up as you age), issue-age (your premium is locked to the age you bought the plan), and community-rated (everyone in your area pays the same, regardless of age). Issue-age plans often look cheaper at first but may cost more over time. Community-rated plans are the same price for everyone, which can be a good deal if you are older.

Most companies offer discounts if you pay the full year upfront instead of monthly, or if you sign up for automatic bank payments. Some also offer discounts for non-smokers. Always ask about these before you decide.

Medigap Plans Work Only With Original Medicare, Not Medicare Advantage

If you have a Medicare Advantage plan (Part C), you cannot buy a Medigap plan. Medicare Advantage is an all-in-one plan run by a private company that includes Part A, Part B, and usually Part D (prescription drugs). It has its own network of doctors and its own out-of-pocket costs. Medigap is designed to fill the gaps in Original Medicare, so the two do not work together.

If you have Medicare Advantage and want to switch to Original Medicare plus a Medigap plan, you can do so during the annual open enrollment period (October 15 to December 7). When you switch, you will have another chance to buy a Medigap plan without health questions, as long as you do it within 63 days of dropping the Advantage plan.

How to Compare Plans and Find the Right One for You

Start by deciding what matters most to you: the lowest monthly premium, the lowest out-of-pocket costs, or a balance of both. If you see many doctors or take many medications, a plan with broader coverage (like Plan G) might save you money overall, even though the monthly premium is higher. If you are healthy and rarely go to the doctor, a basic plan (like Plan A) or a high-deductible plan might be smarter.

Use the Medicare Plan Finder tool on Medicare.gov to see which plans are available in your area and what they cost. You can also call 1-800-MEDICARE to speak with someone who can walk you through the options. Some local Area Agencies on Aging offer free counseling on Medicare choices — search "State Health Insurance information Program" (SHIP) plus your state name to find the one near you.

Once you have narrowed it down to two or three plans, call the insurance companies directly and ask about discounts, customer service ratings, and how they handle claims. Read online reviews, but remember that people who have no problems rarely leave reviews — focus on whether complaints are about the company's response, not just the existence of a problem.

What Happens After You Buy a Medigap Plan

Your Medigap plan and Original Medicare work together automatically. When you go to a doctor who accepts Medicare, you show your Medicare card and your Medigap card. The doctor's office sends the claim to Medicare first. Medicare pays its share and sends the rest to your Medigap company. Your Medigap company then pays what the plan covers. In most cases, you pay nothing at the visit — the two insurers handle it between them.

If you need to switch plans later, you can do so during the annual open enrollment period (October 15 to December 7) or if you have a may have access to life event. When you switch, your new plan starts on the first day of the next month. Your old plan ends automatically, so you do not have to cancel it yourself.

Keep your Medigap card with you at all times, along with your Medicare card. If you move to a new state, check whether your current plan is still available there — some companies do not sell in all states. If your plan is not available in your new state, you have 60 days to buy a different one without health questions.

Frequently Asked Questions

Can I use a Medigap plan with Medicare Advantage?

No. Medigap plans work only with Original Medicare (Part A and Part B). If you have Medicare Advantage, you cannot buy a Medigap plan. If you want Medigap coverage, you must switch to Original Medicare first, which you can do during the annual open enrollment period.

What if I miss my initial enrollment window?

You can still buy a Medigap plan after your window closes, but the insurance company can charge you more or deny coverage based on your health history. Some states have protections that let you buy without health questions at certain times. Contact your state insurance commissioner's office to learn what applies where you live.

Do I still need Part D prescription drug coverage if I have a Medigap plan?

Yes. Medigap covers medical costs, not prescription drugs. You need to buy Part D separately from a private insurance company. You can buy it at the same time as your Medigap plan or later, but if you wait too long, you may pay a penalty.

Can my Medigap premium go up, and how much?

Yes. Premiums can go up each year due to inflation and your age. The amount depends on the pricing method the company uses. Ask your insurance company how much your premium is expected to increase each year so you can budget for it.

What questions should I ask my doctor before choosing a plan?

Ask which Medigap plans their billing staff works with most often, whether they have preferred pharmacies, and whether they expect any major procedures or tests in the next year. This helps you understand which plan will cause the fewest billing headaches and whether a plan with broader coverage makes sense for your situation.