Your share of the costs of a covered health care service, calculated as a percent (for example, 20%) of the allowed amount for the service. You pay co-insurance plus any deductibles you owe. For example, if the health insurance or plan’s allowed amount for an office visit is $100 and you’ve met your deductible, your co-insurance payment of 20% would be $20. The health insurance or plan pays the rest of the allowed amount.