Coinsurance is the amount of money you must pay for a health service, such as a doctor's appointment or a prescription. It's a percentage of the total cost of care. For instance, you may have a 20% coinsurance. If a doctor's visit costs $100, then you pay $20. Your health plan pays $80. You must pay your deductible before the coinsurance rate applies.
Under the Affordable Care Act, health plans cannot charge coinsurance for some services intended to help prevent you from getting a serious illness. For instance, your health plan cannot charge coinsurance for certain cancer screenings or vaccines.