Medicare Coinsurance: Why You Owe 20%

What This Means

Your Medicare Summary Notice or Explanation of Benefits shows a “coinsurance” amount. This is not a denial. Medicare approved your claim and paid its share — the coinsurance is the portion you owe.

For most Part B services (doctor visits, outpatient care, medical equipment), Medicare pays 80% of the approved amount and you pay the remaining 20%. This 20% is your coinsurance.

Why This Happens

• This is standard Medicare cost-sharing. After you meet your annual Part B deductible ($283 in 2026), you pay 20% coinsurance on most Part B services. This is how Original Medicare is designed.
• There is no annual cap on coinsurance in Original Medicare. Unlike Medicare Advantage plans, Original Medicare does not have an out-of-pocket maximum. If you have many or expensive services, your coinsurance can add up throughout the year.
• Part A has different coinsurance rules. For hospital stays, you pay nothing for days 1-60 (after the Part A deductible of $1,736 per benefit period in 2026), then a daily coinsurance for days 61-90 ($434 per day in 2026), and $868 per day for each “lifetime reserve” day (days 91-150, up to 60 days over your lifetime). Skilled nursing facility stays have $0 coinsurance for days 1-20 and $217 per day for days 21-100 in 2026.

Should You Appeal?

What To Do Next

1. Verify the amount. Check that the coinsurance is 20% of the Medicare-approved amount (not the provider’s full charge). The approved amount should be listed on your Medicare Summary Notice.
2. Check if you have supplemental coverage. If you have a Medigap (Medicare Supplement) policy, it likely covers some or all of your Part B coinsurance. Most Medigap plans (A, B, D, F, G, K, L, M, N) cover Part B coinsurance at 50% to 100%. Contact your Medigap insurer to file a claim.
3. Look into the Qualified Medicare Beneficiary (QMB) program. Of the four Medicare Savings Programs, QMB is the one that pays Medicare cost-sharing — Part A and Part B premiums, deductibles, coinsurance, and copays. Federal law also forbids providers from billing QMB enrollees for those amounts. SLMB and QI pay only your Part B premium. Contact your State Health Insurance Assistance Program (SHIP) at shiphelp.org or call 1-800-MEDICARE to apply or check eligibility.
4. If you’re having trouble paying, ask your provider about payment plans. Many providers offer interest-free payment arrangements for Medicare patients.
5. Consider Medigap for future protection. If you are in Original Medicare and do not have supplemental coverage, a Medigap policy can protect you from high coinsurance costs. Note that the best time to enroll is during your Medigap Open Enrollment Period.

Sources

• CMS: 2026 Medicare Parts A & B Premiums and Deductibles — primary source for the 2026 Part A deductible ($1,736), Part B deductible ($283), Part B premium ($202.90), Part A days 61-90 coinsurance ($434/day), lifetime reserve days ($868/day), and SNF days 21-100 coinsurance ($217/day) cited above.
• Medicare.gov: Medicare costs — beneficiary-facing summary of premiums, deductibles, and coinsurance.
• Medicare.gov: What Part B covers — list of Part B-covered services subject to the 20% coinsurance.
• Medicare.gov: Compare Medigap plan benefits — which Medigap plan letters cover Part B coinsurance and at what percentage (Plans K and L are 50% / 75%; the rest are 100%, with small office-visit/ER copays for Plan N).
• Medicare.gov: Medicare Savings Programs — eligibility and benefits for QMB, SLMB, QI, and QDWI.
• CMS: Qualified Medicare Beneficiary (QMB) Program — federal balance-billing prohibition for QMB enrollees.

Frequently Asked Questions