Coinsurance is usually a percentage that you (the insured) must pay. A common coinsurance split is 80/20, meaning that the insurance company pays 80% of your medical bills and you pay 20%. For example, if you went to the ER, and your bill was $1,000, you would pay $200 and your insurance company would pay $800. Coinsurance usually does not apply until you (the insured) have met your deductible.