What is Coinsurance?
Definition
Coinsurance is the percentage of a covered medical bill the member owes after meeting the deductible. Common splits are 80/20 or 70/30, meaning the insurer pays the larger share and the member pays the rest until the annual out-of-pocket maximum is reached.
Real-World Example
After meeting a $2,000 deductible, a $10,000 surgery bill triggers 20% coinsurance. The member pays $2,000 more; the insurer pays $8,000. Once the out-of-pocket maximum caps at $9,100 for 2026, the insurer covers 100% for the remainder of the plan year.
Why It Matters
Coinsurance rules explain why two plans with identical premiums can produce vastly different bills. A plan with 80/20 coinsurance is objectively less generous than 90/10 for high-cost events like childbirth or cancer treatment.
Frequently Asked Questions
Is coinsurance the same as a copay?
No. A copay is a flat dollar amount per visit; coinsurance is a percentage of the total allowed charge.