Coinsurance Calculator: Your Share of a Medical Bill
Work out your coinsurance — the percentage share of a covered medical bill you pay after meeting your deductible — and the amount your health insurer pays.
Adjust the inputs and select Calculate for a full breakdown.
Compare Common Scenarios
How the numbers shift across typical situations for this calculator:
| Scenario | Your coinsurance | Insurer pays |
|---|---|---|
| 20% of $5,000 (you pay $1,000) | 1,000 | 4,000 |
| 10% of $20,000 (you pay $2,000) | 2,000 | 18,000 |
| 30% of $3,000 | 900 | 2,100 |
| 20% of $50,000 (major surgery) | 10,000 | 40,000 |
How This Calculator Works
Enter your coinsurance percentage and the covered (allowed) amount for the service. The calculator returns your coinsurance (your share) and what the insurer pays (the remainder). Coinsurance kicks in after you've met your deductible and applies to the insurer's allowed amount, not always the provider's full sticker charge.
The Formula
Percentage of an Amount
Amount is the base value, Percentage is the rate applied to it
Worked Example
With 20% coinsurance on a $5,000 covered amount, you pay $1,000 and your insurer pays $4,000. Coinsurance is one piece of how health-plan cost-sharing works, alongside the deductible (what you pay before insurance starts paying), copays (flat fees for certain services), and the out-of-pocket maximum (the cap on your total annual cost-sharing). The classic '80/20' plan means the insurer pays 80% and you pay 20% of covered costs after your deductible — until you hit your out-of-pocket max, after which the insurer pays 100%.
Key Insight
Coinsurance is best understood within the full sequence of health-plan cost-sharing, since it doesn't act alone. The order is typically: first you pay your deductible (the full allowed cost up to that amount), then coinsurance kicks in (you and the insurer split covered costs by the coinsurance percentage), and this continues until your total cost-sharing reaches the out-of-pocket maximum, after which the insurer pays 100% for the rest of the year. So this calculator shows the coinsurance split on a covered amount after the deductible is met — your real cost on a given bill also depends on whether the deductible is satisfied and how close you are to your out-of-pocket max. Two crucial points: coinsurance applies to the insurer's allowed (negotiated) amount, which for in-network care is usually far less than the provider's sticker charge — so always use the allowed amount, not the billed amount. And network status matters enormously: out-of-network care often has a higher coinsurance percentage (or isn't covered), and balance billing can leave you owing the difference above the allowed amount. When comparing plans, weigh the coinsurance percentage together with the premium, deductible, and out-of-pocket max — a plan with low coinsurance but a high premium isn't automatically better. Use this to estimate your share of a specific covered bill, and remember the out-of-pocket maximum is your ultimate protection against catastrophic costs in a year.
Frequently Asked Questions
How is coinsurance calculated?
Multiply the covered (allowed) amount by your coinsurance percentage. With 20% coinsurance on a $5,000 covered amount, you pay $1,000 and the insurer pays $4,000. Coinsurance applies after you've met your deductible.
How is coinsurance different from a copay?
A copay is a fixed dollar fee for a service (e.g. $30 for a doctor visit), while coinsurance is a percentage of the covered cost (e.g. 20% of a hospital bill). Copays are predictable flat amounts; coinsurance scales with the size of the bill, so it can be much larger on expensive care.
Does coinsurance apply before or after the deductible?
After. You first pay your deductible (the full allowed cost up to that amount), then coinsurance begins, splitting covered costs between you and the insurer by the coinsurance percentage — continuing until you reach your out-of-pocket maximum, after which the insurer pays 100% for the rest of the year.
What amount does coinsurance apply to?
The insurer's allowed (negotiated) amount, not necessarily the provider's full sticker charge. For in-network care the allowed amount is usually much lower than the billed charge, so use the allowed amount. Out-of-network care can carry higher coinsurance and balance billing above the allowed amount.
What caps my total coinsurance for the year?
Your out-of-pocket maximum — the annual cap on your total cost-sharing (deductible, coinsurance, and copays combined). Once you reach it, the insurer pays 100% of covered costs for the rest of the year. It's your protection against catastrophic medical costs, so factor it in alongside coinsurance when comparing plans.
Related Calculators
Methodology & Review
Coinsurance is your coinsurance percentage applied to the covered (allowed) amount; the remainder is what the insurer pays. It models the coinsurance split on a covered amount after the deductible is met, and does not account for the deductible, copays, or the out-of-pocket maximum.
Written by Ugo Candido · Last updated May 22, 2026.