Coinsurance
Updated September 30, 2026
Definition
Your share of the cost of a covered service, shown as a percentage, like 20%. You usually start paying it after you meet your deductible.
Coinsurance is your share of the cost of a covered service, figured as a percentage. Your plan pays the rest. It usually starts after you've met your deductible. For in-network care, it stops once you reach your out-of-pocket maximum.
The percentage is based on your plan's allowed amount, not the provider's full price. That's why your share can be much smaller than the charge on the bill.
For example, say your plan's allowed amount for an MRI is $1,000 and your coinsurance is 20%. You've already met your deductible, so you pay $200 and your plan pays $800. Your explanation of benefits (EOB) shows this, often in a column for what you may owe. Our guide to comparing your medical bill and EOB shows where to look.
Related terms
Guides that use this term
- GuideMedical bill vs. EOB: how to compare them line by lineYour bill and your EOB should tell the same story. Here's how to compare them in 20 minutes, with a worked example and what to do if they don't match.
- GuideHow to choose a health insurance plan and avoid big billsCompare health plans by total yearly cost, not just the premium. Check networks, doctors, drugs and the SBC, with a worked example and 2027 deadlines.
Sources
- Coinsurance (glossary), HealthCare.gov. Accessed September 30, 2026.
- Out-of-pocket maximum/limit (glossary), HealthCare.gov. Accessed September 30, 2026.
This is general information, not legal or medical advice. Rules can depend on your plan and your state. Romi Care isn't an insurer, law firm, collection agency, or government program.