Copay is the dollar amount you may be required to pay as your share of the cost for a medical service or supply. A copay is usually a set amount, rather than a percentage. For example, you might pay $10 copay for a primary care office visit. Coinsurance is usually a percentage. It is the amount you may be required to pay as your share of the cost for services or prescription drugs. For example, you might pay 20 percent of the cost for a specialist visit.