What Is a Medicare Supplement (Medigap) Plan?

What Does a Medicare Supplement Plan Actually Do?

If you have Original Medicare (Part A for hospital coverage and Part B for medical coverage), you already know it does not pay for everything. You are still responsible for deductibles, copayments, and coinsurance, and those costs can add up fast, especially during a hospital stay or a stretch of ongoing treatment.

A Medicare Supplement plan, commonly called Medigap, is a private insurance policy designed to fill those gaps. It works alongside Original Medicare: Medicare pays its share first, then your Medigap plan kicks in to cover some or all of the remaining costs. Think of it as a financial safety net layered on top of your existing coverage.

Medigap is not the same as Medicare Advantage. Medicare Advantage replaces Original Medicare with a bundled plan from a private insurer. You cannot have both Medigap and Medicare Advantage at the same time.

What Do the Different Medigap Plan Letters Mean?

Medigap plans are standardized by the federal government and labeled with letters: A, B, C, D, F, G, K, L, M, and N. Each letter covers a specific set of benefits, and those benefits are the same regardless of which insurance company sells the plan. In other words, Plan G from one company covers the exact same things as Plan G from another company. The only differences between companies are the premium you pay, the customer service experience, and any discounts they may offer.

Here is a simplified look at the most commonly discussed plans:

• Plan G: The most popular plan for people newly eligible for Medicare. It covers nearly all out-of-pocket costs except the annual Part B deductible ($257 in 2025).
• Plan N: A lower-premium option that covers most costs but may require small copayments for some office visits and emergency room visits that do not result in admission.
• Plan F: The most comprehensive plan, covering all gaps. However, Plan F is only available to people who became eligible for Medicare before January 1, 2020.
• Plans K and L: These plans cover a percentage of costs (50% for K, 75% for L) with an annual out-of-pocket limit, offering lower premiums in exchange for more cost-sharing.

You can view the full comparison chart on Medicare.gov under "Medigap policies" to see exactly what each letter covers.

How Does Medigap Pricing Work?

While benefits are standardized, premiums are not. Insurance companies use one of three pricing methods:

• Community-rated (no-age-rated): Everyone pays the same base premium regardless of age.
• Issue-age-rated: Your premium is based on your age when you first buy the plan and does not increase because you get older (though it may still rise due to inflation or other factors).
• Attained-age-rated: Your premium starts lower but increases as you age. This is the most common method in Oklahoma.

In the Oklahoma City metro area, premiums for the same plan letter can vary significantly from one insurer to another. It is worth getting quotes from multiple companies. Because the coverage is identical, the smartest move is often choosing the lowest-cost carrier with a solid reputation.

What About Rate Increases Over Time?

All Medigap premiums can increase over time due to inflation, rising healthcare costs, and (for attained-age plans) your age. When comparing plans, ask each insurer about their rate increase history over the past five to ten years. This gives you a more realistic picture of what you will actually pay down the road.

When Should You Enroll in a Medigap Plan?

Timing is critical. Your Medigap Open Enrollment Period is the six-month window that begins the month you turn 65 and are enrolled in Medicare Part B. During this period, insurance companies must sell you any Medigap plan they offer at the standard rate. They cannot charge you more or deny you coverage because of pre-existing health conditions.

After this window closes, insurers in Oklahoma can use medical underwriting. That means they can review your health history, charge higher premiums, or refuse to sell you a plan altogether. This is why most Medicare counselors strongly recommend enrolling during your initial Open Enrollment Period, even if you feel healthy.

If you are still working and covered by employer insurance at 65, talk to a Medicare counselor about how to coordinate your enrollment timing so you do not miss this important window.

What Medigap Does Not Cover

It is just as important to know the limits. Medigap plans do not cover:

• Prescription drugs (you need a separate Part D plan)
• Dental, vision, or hearing care
• Long-term care or custodial care
• Private-duty nursing

If any of these are priorities for you, you will need to plan for them separately.

How Oklahoma Residents Can Get Free, Unbiased Help

Choosing the right Medigap plan can feel overwhelming, but you do not have to figure it out alone. Oklahoma offers several free resources:

• Oklahoma SHIP (State Health Insurance Assistance Program): Provides free, one-on-one Medicare counseling. These counselors are trained volunteers who do not sell insurance. Call (800) 763-2828 or visit the Oklahoma Insurance Department website.
• Area Agencies on Aging: The Areawide Aging Agency in Oklahoma City (serving Canadian, Cleveland, Logan, Oklahoma, and surrounding counties) can connect you to local counseling and support services.
• Eldercare Locator: A national service at eldercare.acl.gov or (800) 677-1116 that helps you find local aging resources anywhere in the country.

You can also compare Medigap plan pricing through the official Medicare Plan Finder tool at Medicare.gov.

A Few Smart Steps Before You Decide

• Get quotes from at least three to five insurance companies for the same plan letter.
• Ask about each company's rate increase history.
• Enroll during your Medigap Open Enrollment Period whenever possible.
• Pair your Medigap plan with a Part D prescription drug plan to avoid late enrollment penalties.
• Consider talking to both a SHIP counselor (free, unbiased) and a licensed insurance agent to get different perspectives.

Medicare decisions are some of the most important financial choices you will make in your second half. The good news: with the right information and a little guidance, you can make a confident choice that protects both your health and your budget.

Need help finding a trusted, verified Medicare advisor in the Oklahoma City area or beyond? Second Half 365 connects you with vetted local experts who can walk you through your options, answer your questions, and help you enroll with confidence. Visit our directory to find the right fit for you.