Both copayment and coinsurance refer to a patient’s responsibility for a portion of healthcare costs. A copayment is a set dollar amount that the patient must pay for a specific treatment or medication. Coinsurance is a percentage of the total cost. For example, a very common coinsurance arrangement is that the medical insurance company pays 80 percent of costs for a given therapy, with the patient paying 20 percent. Copayments and coinsurance, along with deductibles, are examples of cost sharing. (FYI, while premiums are paid by the consumer, they are typically NOT considered cost-sharing.)