What a Medicare Supplement Plan Does and Why It Matters

A Medicare Supplement plan (also called Medigap) pays some of the costs that Original Medicare leaves you responsible for — copayments, coinsurance, and deductibles. It does not replace Medicare; it works alongside it. When you see a doctor, Medicare pays its share first, then your Medigap plan pays its share of what remains.

The reason to choose one plan over another comes down to two things: which costs matter most to you, and how much you can afford to pay in monthly premiums. A plan that covers hospital deductibles might cost more per month but save you money if you expect surgery. A plan with lower premiums might leave you paying more out of pocket for doctor visits. Your choice depends on your health, your budget, and how you use medical care.

Key Takeaways

  • Medicare Supplement plans are standardized by the federal government, so Plan G from one insurer covers the same things as Plan G from another — only the price differs.
  • The ten available plans (A, B, D, G, K, L, M, N, and two others) cover different combinations of costs, and not all plans are sold in every state.
  • Your age when you first buy a plan affects your premium for life, so buying during your initial enrollment window (the six months after you turn 65 or first enroll in Medicare Part B) usually costs less than waiting.
  • You can switch plans once per year during the open enrollment period (October 15 to December 7), but you may face medical underwriting if you switch outside that window.
  • Comparing plans means looking at both the monthly premium and what you will pay out of pocket for the services you actually use.

The Ten Standardized Plans and What Each Covers

The federal government defines ten Medigap plans, labeled A through N (with two additional plans, F and G, that have different rules). Each plan covers a fixed set of costs. Plan A is the most basic and cheapest. Plan G covers more than Plan A but costs more per month. This standardization means a Plan G from Aetna covers exactly what Plan G from United Healthcare covers — the only difference is price.

The plans differ in whether they cover the Part B deductible (the amount you pay before Medicare starts paying for doctor visits), the Part A deductible (the hospital deductible), copayments for skilled nursing care, and foreign travel emergency care. Plan N, for example, has lower premiums than Plan G but requires you to pay a copayment at the doctor's office and a higher copayment for emergency room visits. Plan G has no copayments for doctor visits but a higher monthly premium.

Not every plan is sold in every state. Some insurers offer only Plans A, B, and G. Others offer the full range. Your state insurance commissioner's office publishes a list of which plans are available where you live and which insurers sell them. This list changes year to year as insurers enter and leave the market.

How Your Age and Enrollment Timing Affect Your Cost

When you buy a Medigap plan, the insurer sets your premium based on your age at the time you buy it. That age-based premium is locked in — it does not reset if you switch plans later. This means buying during your initial enrollment window (the six months starting the month you turn 65 or the month you first enroll in Medicare Part B, whichever is later) usually results in the lowest premium you will ever pay for that plan.

If you wait to buy a plan after your initial window closes, insurers can charge you more based on how long you waited. Some states allow age-based pricing (your premium goes up each year as you age). Others allow issue-age pricing (your premium is set by your age when you buy and stays the same). A few allow attained-age pricing (your premium rises as you get older, even after you buy). The rules vary by state and by insurer, so the cost of waiting is not the same everywhere.

Medical underwriting is another reason to buy during your initial window. During that window, insurers must sell you a plan without asking health questions. If you wait, they can deny you coverage or charge more if you have a pre-existing condition, depending on your state's rules. Some states protect you from this; others do not.

Comparing Plans by Premium and Out-of-Pocket Costs

Choosing a plan requires looking at two numbers: the monthly premium and what you will actually pay when you use care. A plan with a $150 monthly premium sounds cheaper than one with a $200 premium, but if you see a doctor twelve times a year and the cheaper plan charges a $25 copayment per visit while the expensive plan charges nothing, you will spend $150 more per year on copayments alone.

Start by listing the medical services you use most: doctor visits, hospital stays, specialist care, or prescription drugs (though note that Medigap does not cover prescriptions — that is Part D). Then look up what each plan covers for those services. Many state insurance commissioner websites have comparison charts that show, side by side, what each plan covers. Some insurers' websites also have calculators that estimate your total annual cost (premium plus out-of-pocket) based on your expected use.

If you are healthy and rarely see a doctor, a plan with low premiums and higher copayments might make sense. If you have multiple chronic conditions and see specialists regularly, a plan with higher premiums but lower copayments might save you money overall. The math is personal to your situation.

Where to Find Plans and Compare Prices

Your state insurance commissioner's office publishes a list of Medigap insurers, the plans they sell, and (in many states) the premiums they charge. You can also call 1-800-MEDICARE to request a printed guide or speak with someone who can tell you which plans are sold in your area. Some states run their own comparison websites; others direct you to Medicare.gov's plan finder tool.

When you contact an insurer directly, ask for a quote for each plan you are considering. Premiums vary widely — the same plan can cost $100 per month with one insurer and $180 with another. Getting quotes from at least three insurers is worth the time. Some insurers offer discounts if you pay annually instead of monthly, or if you set up automatic payments.

Be cautious of websites that promise to help you "find the best plan" or "see if you may have access to." Those sites often collect your information and sell it to insurers or brokers. Instead, go directly to your state insurance commissioner's office, call Medicare, or contact insurers by phone or through their official websites.

When You Can Switch Plans and What Happens If You Do

You can switch to a different Medigap plan once per year during the open enrollment period, which runs from October 15 to December 7. If you switch during this window, the new insurer cannot deny you or charge you more based on health. Your coverage starts January 1 of the following year.

If you want to switch outside the open enrollment period, the new insurer can require medical underwriting — meaning they can ask about your health and deny you coverage or charge more if you have a pre-existing condition. Some states have protections that limit this, but not all. Before you switch outside the open enrollment window, contact your state insurance commissioner's office to learn what protections explore where you live.

When you switch plans, your old coverage ends and your new coverage begins on the date the new insurer specifies (usually the first of the month). Make sure your new plan is in place before your old one ends so you have no gap in coverage.

Questions to Ask Your Insurance Agent or Insurer

Before you buy a plan, ask the insurer or agent these questions: What is the monthly premium, and does it ever increase? What is the annual deductible, if any? What copayments or coinsurance will I pay for doctor visits, hospital stays, and specialist care? Does the plan cover the Part B deductible? Does it cover skilled nursing care? Is there a limit on how much the plan will pay in a year? What happens if I need care outside the United States?

Also ask: Can I switch plans later if my needs change? What is the process for filing a claim? Does the plan have a network of doctors, or can I see any doctor who accepts Medicare? (Most Medigap plans have no network — you can see any doctor who accepts Medicare.) If the insurer denies a claim, what is the appeal process?

Frequently Asked Questions

Can I buy a Medigap plan if I already have a Medicare Advantage plan?

No. You can have either Original Medicare with a Medigap plan, or a Medicare Advantage plan, but not both. If you have a Medicare Advantage plan and want to switch to Original Medicare with Medigap, you have a limited window to do so without medical underwriting. Contact Medicare or your state insurance commissioner's office to learn the exact dates.

Do all Medigap plans cover prescription drugs?

No. Medigap plans do not cover prescription medications. If you take prescription drugs, you need to enroll in a separate Medicare Part D plan. You can have both a Medigap plan and a Part D plan at the same time.

What if I move to a different state?

Your Medigap plan may not be sold in your new state. You will likely need to switch to a plan that is available there. Contact your current insurer to ask about your options, and contact your new state's insurance commissioner's office to see which plans are sold there. You may be able to switch without medical underwriting if you move.

Does my Medigap plan cover dental, vision, or hearing care?

No. Medigap plans do not cover dental, vision, or hearing services. Original Medicare does not cover these either. You can buy separate dental, vision, or hearing plans if you need them, but they are not part of Medigap.

What happens to my Medigap plan if I go back to work and get health insurance through my employer?

You can keep your Medigap plan while you have employer coverage, but you will pay premiums for both. If you later drop the employer plan and want to return to your Medigap plan, you may face medical underwriting depending on how long you were away. Ask your Medigap insurer about your options before you make a change.