What a Medicare Supplement Plan Does and Why It Matters

A Medicare Supplement plan (also called Medigap) covers costs that Original Medicare leaves you responsible for: deductibles, copayments, and coinsurance. Original Medicare pays a percentage of your doctor and hospital bills, but you pay the rest out of pocket. A supplement plan fills those gaps by paying those amounts directly to the provider or to you.

The choice between supplement plans affects how much you spend each month in premiums and how much you pay when you actually use care. A plan with a higher monthly premium might save you money overall if you see doctors frequently. A plan with a lower premium might work better if you rarely need care. The right choice depends on your health, your budget, and how much financial predictability matters to you.

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 premium price differs.
  • You have the best chance of being accepted without medical underwriting during your open enrollment period: the six months after you turn 65 and enroll in Medicare Part B.
  • Plan G and Plan N are the most common choices for new enrollees because they offer broad coverage at reasonable cost, though the best plan for you depends on your health and spending patterns.
  • Your premium will vary by insurer, location, and age, so comparing quotes from at least three companies before you choose is worth the time.
  • You can switch plans once per year during the annual open enrollment period (October 15 to December 7), but switching outside that window may require medical underwriting.

The Ten Standardized Plans and What Each Covers

The federal government defines ten standardized Medicare Supplement plans: A, B, D, G, K, L, M, and N. (Plans C and F were discontinued for people who became may be able to access for Medicare after January 1, 2020.) Each plan letter covers a specific set of costs. An insurer cannot change what Plan G covers — they can only set the price. This means you can compare plans across different insurance companies knowing that the coverage is identical.

Plan A is the most basic and least expensive. It covers coinsurance for hospital stays and some doctor visits, but not the Part B deductible. Plan G covers nearly everything except the Part B deductible (which is $240 in 2024, though this amount changes yearly). Plan N covers most costs but charges you a small copayment for doctor visits and emergency room visits. Plans K and L cover a percentage of costs rather than all costs, making them cheaper but leaving you with more out-of-pocket spending. Plans B, D, and M are less common and cover specific gaps that appeal to fewer people.

The best way to understand which plan fits your situation is to list the costs you expect to pay under Original Medicare, then see how each plan would change that number. If you have frequent doctor visits, a plan that covers copayments (like Plan G or N) will save you more than a plan that does not.

When You Have the Best Chance of Being Accepted

Insurance companies can refuse to sell you a supplement plan or charge you more based on your health history — a practice called medical underwriting. However, federal law gives you a window when they cannot do this: the six months after you enroll in Medicare Part B. This period is called your open enrollment period, and it is the single best time to buy a supplement plan.

If you miss this window, you can still buy a plan, but the insurer may ask health questions, order medical records, or deny you coverage altogether. Some states have additional protections that extend may provide issue rights beyond six months, so check your state's rules. If you are denied by one company, other companies may still accept you, though at a higher premium.

Your open enrollment period starts the first day of the month you turn 65 or the month you enroll in Part B, whichever is later. If you turn 65 in March and enroll in Part B that same month, your six-month window runs from March through August. Mark this on your calendar, because once it closes, your options narrow significantly.

How to Compare Plans and Get Quotes

Start by deciding which plan letter appeals to you based on the coverage it offers. Most people choose between Plan G (broadest coverage) and Plan N (lower premium, small copayments). Once you have narrowed it down, contact at least three insurance companies that sell supplements in your state and ask for a quote for that specific plan.

The companies you contact do not have to be national names. Many regional and local insurers sell supplement plans and sometimes offer lower premiums than larger companies. Your state health insurance counselor (find yours through your State Health Insurance information Program, or SHIP) can tell you which companies are licensed in your state and help you understand quotes.

When you get quotes, compare the monthly premium, the annual deductible (if any), and any waiting periods for pre-existing conditions. Write down the company name, the plan letter, the monthly premium, and the effective date. Premiums change, so get quotes close to the time you plan to enroll. Some companies offer discounts if you pay annually instead of monthly, or if you enroll online, so ask about those too.

Age, Location, and How Insurers Price Plans

Your premium depends on three things: the plan you choose, your age, and where you live. Some insurers use age-attained pricing, meaning your premium goes up each year on your birthday. Others use issue-age pricing, meaning your premium is based on your age when you first enroll and stays the same relative to that age. A third method, community rating, charges everyone in your state the same price regardless of age. Each method produces different costs over time, so a plan that looks cheapest at 65 might be expensive by 75.

Location matters because each state sets its own rules for supplement plans, and insurers price differently in different regions. A plan that costs $150 per month in one county might cost $180 in another county fifty miles away. This is why getting quotes specific to your zip code is important.

Your health history does not affect your premium during your open enrollment period, but it may affect whether you are accepted at all if you explore outside that window. Once you are enrolled, your health does not change your premium — only your age and the plan's pricing method do.

Making Your Choice and Enrolling

After you have compared quotes, choose the plan and company that offers the best combination of premium, coverage, and pricing method for your situation. If you are still working or have other health coverage, you might choose a less comprehensive plan to save on premiums. If you have chronic conditions and see doctors regularly, a comprehensive plan like Plan G might save you money overall despite a higher monthly cost.

Contact the insurance company directly to enroll. You can usually do this online, by phone, or by mail. You will need your Medicare number (on your Medicare card), your Social Security number, and information about any other health coverage you have. The company will ask your effective date — this is usually the first day of the month after you submit your process, though some companies offer earlier dates if you explore early in the month.

Once you are enrolled, the insurance company will send you an ID card and a summary of benefits. Keep your Medicare card and your supplement card with you when you see doctors. Tell your provider's billing office that you have a supplement plan so they can bill the supplement company after Medicare pays its share.

Switching Plans or Changing Your Mind

You can switch to a different supplement plan once per year during the annual open enrollment period for Medicare Supplement plans, which runs from October 15 to December 7. If you switch during this window, the new plan becomes effective January 1, and you do not face medical underwriting. Outside this window, switching requires medical underwriting, and you may be denied or charged more.

If you enroll in a plan and change your mind within 30 days, you have a right to cancel and get your money back. This grace period gives you time to make sure you chose the right plan. After 30 days, cancellation is permanent unless you are switching during the annual open enrollment period.

If your circumstances change — you move to a different state, your health worsens, or you find a plan with better coverage at a lower price — contact your state's SHIP program. They can help you understand whether switching makes sense and guide you through the process.

Frequently Asked Questions

Can I have both a Medicare Supplement plan and a Medicare Advantage plan?

No. You choose either Original Medicare with a supplement plan, or a Medicare Advantage plan. You cannot have both at the same time. If you have a supplement and want to switch to Advantage, you must drop the supplement first. If you later switch back to Original Medicare, you may face medical underwriting when you try to buy a supplement again.

What happens to my supplement plan if I move to a different state?

Your plan may not be available in your new state, or the premium may change. Contact your insurance company as soon as you know you are moving. They will tell you whether your plan continues or whether you need to switch. If you must switch, you may be able to do so without medical underwriting if you are moving within your open enrollment period.

Do supplement plans cover prescription drugs?

No. Supplement plans cover only the gaps in Original Medicare's hospital and doctor coverage. Prescription drug coverage comes from a separate plan called Part D. You choose a Part D plan during the same enrollment period as your supplement plan, and you can switch Part D plans once per year.

Will my premium go up every year?

Yes, but the reason depends on your plan's pricing method. With age-attained pricing, your premium rises on your birthday. With issue-age pricing, your premium may rise due to inflation or claims experience, but not because of your age. With community rating, everyone's premium rises together. Ask your insurer which method they use before you enroll.

What if I cannot afford the monthly premium?

Some states offer programs that help pay supplement premiums for people with low income. Contact your state's SHIP program or your local Area Agency on Aging to learn whether you may have access to. You can also choose a less comprehensive plan (like Plan K or L) to lower your monthly cost, though you will pay more when you use care.