What does Coinsurance mean?

Coinsurance is percentage-based cost sharing for a covered service. It is generally calculated from the health plan's allowed amount, not automatically from the provider's original charge. In a synthetic example, if a plan allowed $200 and assigned 20% coinsurance after any applicable deductible, the calculated coinsurance would be $40. Real claims can include multiple lines, separate facility and professional services, or other benefit rules, so the EOB controls the plan's calculation.

Coinsurance commonly applies after an applicable deductible has been met, but plan designs differ. The percentage can change with network status, service category, or tier, and an out-of-network provider may also seek an additional balance when billing is permitted. Check the EOB for the allowed amount and the portion assigned to coinsurance, then compare those figures with the provider bill. Ask the plan which benefit and network rule it used if the percentage or calculation is unclear. A displayed percentage alone does not establish the final legal amount owed.