Coinsurance Calculator
Reviewed by Hamza Gujjar, Algorithm Architect & Software Developer
Last updated: July 27, 2026Coinsurance Calculator
Coinsurance is distinct from a copay - rather than a flat dollar fee, it's a percentage of the bill you owe after meeting your deductible. This calculator walks through the full cost-sharing calculation.
Formula
- Apply remaining deductible to the bill
- Coinsurance Owed = (Bill - Deductible Applied) x Coinsurance%
- Total Owed = Deductible Applied + Coinsurance Owed, capped at remaining out-of-pocket maximum
Example
$5,000 bill, $500 remaining deductible, 20% coinsurance, $3,000 remaining out-of-pocket max:
Deductible Applied = $500 → Coinsurance Owed = $900 → Total Owed = $1,400
The Common 80/20 Structure
A frequently seen coinsurance structure is 80/20, meaning insurance pays 80% of the bill after the deductible and you pay the remaining 20% - other common splits include 70/30 and 90/10, generally trading a higher monthly premium for a more favorable (lower) coinsurance percentage.
Why the Out-of-Pocket Maximum Matters
The out-of-pocket maximum acts as a hard annual ceiling on your total cost-sharing responsibility - once your combined deductible and coinsurance payments reach that limit, insurance covers 100% of covered costs for the remainder of the plan year, which is exactly why this calculator caps the final owed amount at that figure.