Coinsurance
Definition current for the 2026 plan year · Last reviewed July 2026
In one sentence: Your percentage share of a medical bill after the deductible — e.g., you pay 20%, the plan pays 80%.
Coinsurance is the percentage of a bill you pay after meeting your deductible. A "20% coinsurance" plan means: deductible first, then you pay 20% of each covered bill and the plan pays 80%, until you hit your out-of-pocket maximum.
Coinsurance is where big-ticket surprises live, because percentages of large numbers are large: 20% of a $60,000 surgery is $12,000 — which is why the OOPM ceiling matters more than the coinsurance rate itself. Bronze plans often carry 40–50% coinsurance, effectively meaning you pay most of everything until the OOPM.
Compare with a copay — a flat fee per service that doesn't depend on the bill. A plan quoting friendly copays for office visits may still use harsh coinsurance for hospital care, imaging, and specialty drugs — those three lines are where to read the fine print.