How Medigap Plans Work With Original Medicare

If you choose to stay on Original Medicare (Parts A and B) rather than enrolling in a Medicare Advantage plan, you will notice that there are still costs left over — deductibles, copays, and coinsurance that can add up, especially if you need frequent care or face a hospital stay.

That is where Medigap comes in. Medigap plans, also called Medicare Supplement plans, are private insurance policies designed specifically to help cover those remaining costs.

What Medigap Covers

Medigap plans work alongside Original Medicare. After Medicare pays its share of a covered service, your Medigap plan kicks in to help pay some or all of the rest. Depending on the plan letter you choose, Medigap can cover:

• Part A hospital deductible
• Part A coinsurance for extended hospital stays
• Part B coinsurance (the 20% you would normally pay)
• Part B excess charges (from providers who charge more than the Medicare-approved amount)
• Skilled nursing facility coinsurance
• First three pints of blood
• Foreign travel emergency coverage

The most popular plan today is Plan G, which covers all of the above except the Part B annual deductible ($283 in 2026). This means that after paying the annual Part B deductible, you would have little to no additional cost-sharing for Medicare-covered services.

What Medigap Does NOT Cover

Medigap has clear limits. It does not cover:

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

Medigap is strictly a companion to Original Medicare — it fills the gaps in Part A and Part B coverage, nothing more.

How Medigap Plans Are Standardized

Medigap plans are identified by letters: Plan A, Plan B, Plan C, Plan D, Plan F, Plan G, Plan K, Plan L, Plan M, and Plan N. Each letter provides a defined set of benefits, and those benefits are the same regardless of which insurance company sells the plan.

For example, Plan G from one insurer covers exactly the same benefits as Plan G from another. The only differences between companies are:

• The premium amount
• Rate increase history
• Customer service quality

This standardization makes Medigap easier to compare than many other types of insurance.

• Medigap works with Original Medicare to help cover the deductibles, copays, and coinsurance that Parts A and B leave behind.
• Plans are standardized by letter — the benefits within each letter are identical across insurers, so you are really comparing price and company.
• Medigap does not include drug coverage — you will need a separate Part D plan for prescriptions.

When to Enroll in Medigap

The best time to enroll in a Medigap plan is during your Medigap Open Enrollment Period — the six-month window that starts the month your Part B coverage is effective and you are 65 or older.

During this window:

• You have guaranteed-issue rights, meaning insurers cannot deny you coverage or charge more based on health conditions
• You can enroll in any Medigap plan sold in your state without medical underwriting

Outside of this window, insurers in Kentucky can require medical underwriting, which means they can charge higher rates or deny coverage based on your health history. This makes the open enrollment period particularly important for anyone considering the Medigap path.

Summit Benefits Group walks clients through this timeline so they understand exactly when their window opens and what steps to take.

How Medigap Premiums Work

Medigap premiums are set by the insurance company and can be structured in different ways:

• Community-rated — everyone pays the same premium regardless of age
• Issue-age-rated — your premium is based on your age when you first buy the policy and does not increase due to aging (though it may increase for other reasons like inflation)
• Attained-age-rated — your premium is based on your current age and can increase as you get older

Understanding the rating method is important because it affects how your costs may change over time. A lower starting premium with attained-age rating may eventually cost more than a higher starting premium with issue-age rating.

Medigap vs Medicare Advantage: A Quick Note

You cannot have both Medigap and Medicare Advantage at the same time. If you enroll in a Medicare Advantage plan, your Medigap policy will not pay benefits. These are two separate paths:

• Medigap + Original Medicare + Part D = maximum flexibility, higher premiums, predictable costs
• Medicare Advantage = bundled coverage, lower premiums, network-based care

For a detailed comparison of these paths, see our guide on Medicare Advantage vs Medigap.

Related Reading

Once you understand how Medigap pairs with Original Medicare, the next step is usually choosing a letter — understanding Medigap plan letters explains what Plan G, N, and the others actually standardize. If you are still deciding between the two coverage paths, Medicare Advantage vs Medigap: which fits and our Medigap page are the places to start.

Medigap decisions are best made with a clear understanding of the plan options, the timing, and the long-term cost picture. At Summit Benefits Group, we compare Medigap plans for Kentucky clients based on their specific situation — including health history, budget, and how they prefer to use healthcare.

We explain the differences between plan letters, compare premiums from multiple insurers, and help you understand the enrollment timeline so nothing falls through the cracks.