After you meet your plan's deductible, you'll either pay for your care with copays or coinsurance. Many plans include a mix of both, where you pay copays for routine care (like doctor's visits and prescriptions), and coinsurance for more specialized services (like X-rays and surgery). Coinsurance is a percentage of each service’s total cost that you’ll pay. If your coinsurance is 30% for an office visit, then you pay 30% of whatever the doctor charges and your carrier pays the other 70%.
For medical plans, you pay nothing for in-network preventive care, regardless of your deductible.
Coinsurance example: Chelsea just got an MRI. Her deductible was already met, so instead of being charged the total amount, she pays coinsurance. Her 30% coinsurance means that she'll pay $975 instead of the entire $3,250 price tag. This amount goes toward her out-of-pocket maximum, which is the greatest amount she'll have to pay for medical expenses this year.