A copay is a fixed amount (such as $30, for example) paid by a patient for receiving a particular health care service, with the remaining balance covered by the person's insurance company. It is a flat fee assessed to the patient by the insurance company at each visit. The patient should pay this fee to the provider at the time of each visit.
Coinsurance is the percentage of costs of a covered health care service you pay (20%, for example) after you've paid your deductible. It is the percentage of a visit not paid for by insurance. Coinsurance is the amount that the patient owes the provider and must pay each visit. Your insurance policy determines which and how much will be due. Some people may have a deductible that is due before the coinsurance will go into effect.