Coinsurance Law and Legal Definition

Coinsurance is a clause in a medical insurance policy requires the patient to pay x percent of the cost of medical treatment, or a fixed payment per prescription. This is often coupled with a deductible where the patient pays the first y dollars of a given medical treatment or the first y dollars of medical treatment within a given period (usually a calendar year.

For instance, an insured may be required to pay 20% of a doctor's office visit, after the yearly deductible is met. If the deductible is $100 and the office visit is $250, the patient pays $100 for the deductible and $30 of the remaining $150 as coinsurance. Coinsurance is also referred to as copayment.