GLOSSARY · HEALTH

Coinsurance

Percentage of cost you share with insurance after meeting your deductible.

Health 📋 Reviewed by InsureCo Editorial Team · Updated April 30, 2026
Quick definition: Percentage of cost you share with insurance after meeting your deductible.

Full explanation

Coinsurance is the percentage of a service's cost you pay after meeting your deductible — common percentages: 10%, 20%, 30%, 40%. Insurance pays the rest. For example, on a 20% coinsurance plan, after deductible you pay $200 of a $1,000 service. Coinsurance applies up to the out-of-pocket maximum, after which insurance covers 100% for the rest of the year. Original Medicare Part B uses 20% coinsurance with NO out-of-pocket maximum, which is why most people pair it with Medigap or Medicare Advantage.

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