There is no single "best" Medicare supplement — the right one depends on what you use the doctor for and how much you want to pay each month

A Medicare supplement (also called Medigap) is insurance you buy from a private company to cover costs that Original Medicare leaves behind: copayments, coinsurance, and deductibles. Medicare itself does not sell these policies. The "best" one for you is the one that covers the gaps you actually face — not the one with the most coverage or the lowest price alone, but the one that balances what you need with what you can afford to pay in premiums.

The federal government sets what each supplement plan covers, so a Plan G from one company covers exactly the same things as a Plan G from another company. The difference is price. This means you are really choosing between two things: which letter plan fits your medical life, and which company offers it cheapest in your area.

Key Takeaways

  • Medicare supplements are sold by private insurance companies, not Medicare, and cover the copayments and deductibles that Original Medicare does not pay.
  • The federal government defines what each lettered plan (A, B, D, G, M, N) covers, so the same plan letter is identical across all companies — only the monthly premium differs.
  • Plan G and Plan N are the most common choices today because older plans (like Plan F) are no longer sold to people new to Medicare.
  • You can switch plans during the annual open enrollment period (October 15 to December 7) or within 63 days of turning 65 or first joining Medicare Part B.
  • Comparing quotes from at least three companies in your state is the only way to find the lowest price for the plan you choose.

How the lettered plans differ

Each plan letter covers a different combination of the costs Medicare leaves behind. Plan A is the most basic and cheapest. Plan G covers nearly everything except the Part B deductible (the amount you pay before Medicare starts paying). Plan N is similar to G but charges you a small copayment at the doctor's office and for emergency room visits, which brings the monthly premium down.

Plan F used to be the most popular because it covered everything, but it is no longer sold to anyone new to Medicare — only to people who had it before January 1, 2020. If you are new to Medicare or switching plans, you will not see Plan F as an option.

The other plans (B, D, M) exist but are rarely chosen because they leave larger gaps unfilled. Most people who shop around end up choosing Plan G or Plan N. Your choice between them usually comes down to whether you see the doctor often enough that the small copayments in Plan N add up to more than the premium difference between the two plans.

When you can buy or switch a supplement

The best time to buy a Medicare supplement is within 63 days of turning 65 or first joining Medicare Part B. During this window, insurance companies must sell you a plan at their standard rate — they cannot charge you more because of health problems you have. This is called may provide issue rights.

After that window closes, insurance companies can deny you coverage or charge you more based on your health history. You can still buy a supplement, but you may not get the same price or approval.

You can switch to a different supplement plan during the annual open enrollment period, which runs from October 15 to December 7 each year. Changes take effect on January 1. Outside this window, switching is difficult and may require medical underwriting, meaning the company reviews your health before deciding whether to sell you a plan.

How to compare prices in your state

Because the coverage is identical across companies for each plan letter, the only reason to choose one company over another is price. A Plan G from Company A might cost $120 a month while the same plan from Company B costs $160. That $40 difference adds up to $480 a year.

You can get quotes by calling insurance companies directly, but the faster way is to use your state's health insurance counseling program. Each state runs a program (often called SHIP, the State Health Insurance information Program) that provides free, unbiased counseling and can show you quotes from multiple companies at once. Search online for "[your state] SHIP" or call 1-800-MEDICARE to find your state's program.

When you compare, make sure you are looking at the same plan letter from each company. Write down the monthly premium, the deductible (if any), and any waiting periods for pre-existing conditions. Then choose the lowest price for the plan you want.

What a supplement does and does not cover

A Medicare supplement pays toward the costs that Original Medicare does not fully cover: the Part B deductible, copayments for doctor visits, coinsurance for hospital stays, and excess charges if a doctor does not accept Medicare's approved amount. Depending on the plan, it may also cover some costs abroad if you need emergency care while traveling outside the United States.

What it does not cover: prescription drugs, dental, vision, hearing aids, or long-term care. If you need prescription drug coverage, you buy that separately through a Part D plan. If you want dental or vision coverage, you would need to buy a separate policy or join a Medicare Advantage plan instead (which is a different type of Medicare insurance altogether).

Supplement versus Medicare Advantage

A Medicare supplement works alongside Original Medicare — you keep your Medicare card and see any doctor who accepts Medicare. A Medicare Advantage plan is a different product. It replaces Original Medicare and usually includes prescription drug coverage, dental, and vision, but it limits you to a network of doctors and requires referrals for specialists.

Neither is "better" — they suit different people. If you like your doctors and want to see any specialist without a referral, a supplement with Original Medicare is usually the right choice. If you want everything bundled into one plan and do not mind a network, Advantage might work for you. You can switch between them during the annual open enrollment period.

Common reasons people switch supplements

Some people switch because their premium went up. Insurance companies raise rates every year, and sometimes a competitor's Plan G becomes cheaper than what you are paying. It is worth checking prices every year during open enrollment.

Others switch because their health or doctor situation changed. If you now see a specialist who charges more than Medicare's approved amount, a plan that covers excess charges becomes more valuable. If you moved to a different state, prices and available plans change.

A few people switch from a supplement to Medicare Advantage or vice versa, usually because their needs changed — for example, they developed a chronic condition that requires many prescriptions, making the bundled drug coverage in Advantage appealing.

Frequently Asked Questions

Can I buy a supplement if I have a pre-existing condition?

Yes, but the timing matters. If you buy within 63 days of turning 65 or joining Part B, companies must sell to you regardless of health history. After that, they can deny you or charge more. If you are past that window and have been denied, ask your state's SHIP program about your options — some states have additional protections.

Do I need a supplement if I have Medicare Advantage?

No. Medicare Advantage plans include coverage for copayments and coinsurance within the plan. Buying a supplement on top of Advantage is usually not allowed and would be a waste of money. Supplements are for people with Original Medicare.

What happens to my supplement if I move to another state?

Your current plan may not be available in your new state, or the price may be very different. You can switch to a different plan during open enrollment without medical underwriting. Contact your state's SHIP program to see what plans are available where you are moving.

Can I switch supplements outside the open enrollment period?

Switching outside October 15 to December 7 is possible but difficult. The new company can require medical underwriting, meaning they review your health and may deny you or charge more. Your best option is to wait for open enrollment unless your situation is urgent — ask your current company or SHIP whether you may have access to for an exception.

Will my supplement premium go down if I am healthy?

No. Once you own a supplement, your premium is based on your age and the plan you chose, not on how often you use it or how healthy you are. Premiums rise with age and when the insurance company raises rates for everyone on that plan.