Coinsurance is the percentage of coverage provided by health insurance companies, after co-payments or deductibles have been met. For example, a 25% coinsurance rate means that you are responsible for paying 25% of any medical costs incurred. Specifically, $75 of a $100 medical bill would be covered by the insurance company, and your out-of-pocket cost would be $25. It is important to note that each insurance company has its own combination of co-payments, deductibles, and coinsurance.