Coinsurance requires the insured to share in the cost of medical care. Under an 80/20 coinsurance provision, the medical carrier pays 80% of eligible medical charges above any deductible. The insured is required to pay the remaining 20%. Other coinsurance arrangements (e.g., 70/30 or 90/10) are sometimes used.

There is usually a coinsurance provision that places a limit on the insured's out-of-pocket costs in a given year. The size of the coinsurance cap generally ranges from $2,000 to $3,000, depending on the plan, although limits as low as $1,000 are sometimes used. Once the coinsurance cap has been reached, all eligible expenses above this amount are paid in full, up to the plan's overall limit of coverage.