Medicare's 20% Coinsurance Has No Annual Cap — Here's What That Means

Most health insurance plans cap what you owe each year. Hit the out-of-pocket maximum and the plan covers everything after that. Original Medicare doesn't work this way — and the surprise hits hardest when a parent needs serious medical care.

The 20% Problem

After your parent meets the $283 annual Part B deductible, Original Medicare pays 80% of the Medicare-approved amount for outpatient services, doctor visits, durable medical equipment, lab tests, and outpatient procedures. Your parent owes the remaining 20%.

There is no annual limit on that 20%.

A $10,000 outpatient surgery means $2,000 in coinsurance. A $100,000 cancer treatment means $20,000. A year of ongoing chemotherapy, physical therapy, and specialist visits can pile up coinsurance obligations that dwarf a fixed-income senior's entire annual Social Security benefit.

Private employer plans and Medicare Advantage plans must cap out-of-pocket spending (the Medicare Advantage limit varies by plan and year). Original Medicare has no equivalent protection.

Part A Has Its Own Exposure

The coinsurance problem extends beyond Part B. For hospital stays under Part A:

• Days 1–60: Your parent pays the $1,736 inpatient deductible per benefit period — and a new benefit period starts after 60 consecutive days out of the hospital
• Days 61–90: $434/day in coinsurance
• Days 91–150 (lifetime reserve days): $868/day in coinsurance
• Beyond 150 days: Medicare pays nothing

A severe illness requiring 90 days of hospitalization costs your parent $1,736 + (30 × $434) = $14,756 — before any outpatient follow-up care.

Three Ways to Close the Gap

1. QMB (Qualified Medicare Beneficiary) QMB is the most comprehensive solution for low-income beneficiaries. It covers all deductibles, coinsurance, and copayments — Part A and Part B. If your parent qualifies (income under $1,350/month individual, with state variations), their out-of-pocket Medicare costs drop to effectively zero.

QMB also provides balance billing protection: providers cannot bill QMB patients for any amount beyond what Medicare and Medicaid pay, even if the provider doesn't participate in Medicaid.

2. Medigap (Medicare Supplement Insurance) For parents whose income is too high for QMB, Medigap policies fill the coinsurance gap. Plan G — the most popular — covers the Part A deductible, Part B coinsurance (the uncapped 20%), Part A coinsurance for extended hospital stays, and the first three pints of blood.

Medigap premiums vary by state, age, and health status. In many states, a 65-year-old pays $100–$200/month. The trade-off is clear: pay a predictable monthly premium to eliminate unpredictable coinsurance exposure.

3. Medicare Advantage (Part C) Medicare Advantage plans replace Original Medicare with private insurance that includes a mandatory out-of-pocket maximum that varies by plan and year. The cap provides catastrophic protection, but Advantage plans come with network restrictions, prior authorization requirements, and varying quality by region.

Why This Matters for Caregivers

The uncapped coinsurance is the single biggest financial risk in Original Medicare for a parent without supplemental coverage. A parent managing multiple chronic conditions — diabetes, heart disease, arthritis — can accumulate thousands in coinsurance annually from routine care alone, not just from emergencies.

If your parent is on a fixed income and enrolled in Original Medicare without Medigap, check their eligibility for QMB or another Medicare Savings Program. The premium savings alone are significant, but the coinsurance elimination is where the real financial protection lives.

See more United States guides →