Coinsurance

Coinsurance is the percentage of a medical bill you pay after meeting your deductible, with the insurer covering the rest. A common structure is 20 percent coinsurance, meaning you pay 20 percent of the bill and your plan pays 80 percent, up to your annual out-of-pocket maximum.

Coinsurance is harder to budget for than a flat copay because the dollar amount scales with the cost of care. A single MRI at $4,000 with 20 percent coinsurance is $800 out of pocket. Knowing this in advance is why upfront cost estimates matter.