Copayment is a specified amount that you pay for a service or product, such as $10 for an office visit, $12 for a prescription, etc. Payment is usually required at the time you receive the service or product is received.
Coinsurance is a percentage of the total cost of the service received. Plans identified as 80-20 refer to such cost-sharing arrangements (80 percent of fee paid by the plan, 20 percent paid by you). Both copayments and coinsurance are out-of-pocket costs.