What does the term coinsurance represent in health insurance cost-sharing structures?

Paying a percentage of the allowed cost of a service after meeting the deductible.

Coinsurance is a form of cost-sharing where the insured individual is responsible for paying a specified percentage of the allowed charges for a covered service, but this payment obligation only begins after the annual deductible has been fully satisfied. For instance, in an 80/20 coinsurance arrangement, the insurer covers 80% of the allowed amount for the service, leaving the remaining 20% as the policyholder's responsibility. This mechanism differs fundamentally from a copayment, which is a fixed dollar amount paid per service, and the deductible, which is a cumulative out-of-pocket threshold that must be crossed before coinsurance applies. Understanding this percentage share is vital for forecasting expenses for ongoing treatments or significant procedures.