Coinsurance Calculator
Estimate your share of a medical bill: the deductible you pay first, your coinsurance percentage after that, and how the out-of-pocket maximum caps your total cost.
How to use this tool
- Enter the insurer-allowed amount for the medical care.
- Enter the deductible you still have left to meet this year.
- Enter your coinsurance percentage and your remaining out-of-pocket maximum.
- Read what you pay versus what the insurer pays.
Coinsurance is the percentage of a medical bill you keep paying after you have met your deductible — until you hit your out-of-pocket maximum. This calculator walks the bill through all three layers: deductible first, then your coinsurance share, then the cap that stops your spending for the year.
Formula
Cost-sharing after the deductible
Deductible paid = min(Bill, Remaining deductible)
Coinsurance = (Bill − Deductible paid) × Coinsurance%
You pay = min(Deductible paid + Coinsurance, Out-of-pocket max)
Insurer pays = Bill − You pay
The out-of-pocket maximum is a hard cap: once your spending reaches it, the insurer pays 100% of further allowed costs.
How it works
A health plan splits a covered bill in a fixed order. First you satisfy any remaining deductible out of your own pocket. Once that is met, you and the insurer share the rest according to the coinsurance split — for example, you pay 20% and the plan pays 80%. Finally, the out-of-pocket maximum caps your total annual spending; this calculator applies that cap to the combined deductible-plus-coinsurance figure so your payment never exceeds it.
The calculation uses the insurer-allowed amount rather than the provider's list price, because in-network coverage is based on negotiated rates. It assumes the deductible and out-of-pocket figures you enter are the amounts still remaining for the year, so partial-year usage is handled by adjusting those inputs. Copays for specific services and bills from out-of-network providers follow different rules and are not modeled here.
This is general information, not medical or insurance advice. Real plans vary in how deductibles, copays, and embedded family limits interact. Check your Summary of Benefits and Coverage or call your insurer to confirm how a specific claim will be paid.
Worked example
$10,000 bill with $2,000 deductible left and 20% coinsurance
- Pay the remaining deductible: min($10,000, $2,000) = $2,000.
- Coinsurance on the rest: ($10,000 − $2,000) × 20% = $8,000 × 0.20 = $1,600.
- Your total: $2,000 + $1,600 = $3,600, which is below the $6,000 cap.
- Insurer pays the remainder: $10,000 − $3,600 = $6,400.
You pay: $3,600.00
Your cost on a $10,000 bill ($2,000 deductible, $6,000 OOP max)
| Coinsurance | Deductible | Coinsurance amount | You pay |
|---|---|---|---|
| 0% | $2,000.00 | $0.00 | $2,000.00 |
| 10% | $2,000.00 | $800.00 | $2,800.00 |
| 20% | $2,000.00 | $1,600.00 | $3,600.00 |
| 30% | $2,000.00 | $2,400.00 | $4,400.00 |
| 50% | $2,000.00 | $4,000.00 | $6,000.00 |
Key terms
- Coinsurance
- The percentage of a covered medical cost you pay after meeting your deductible, with the insurer paying the rest.
- Deductible
- The amount you must pay yourself before your plan starts sharing costs through coinsurance.
- Out-of-pocket maximum
- The most you can pay in a plan year; once reached, the insurer covers 100% of further allowed costs.
- Allowed amount
- The maximum a plan will count for a covered service — usually the in-network negotiated rate, not the list price.
Frequently asked questions
- What is the difference between coinsurance and a copay?
- A copay is a flat dollar amount for a service (e.g. $30 for a visit). Coinsurance is a percentage of the bill that you pay after meeting your deductible.
- Does coinsurance count toward my out-of-pocket maximum?
- Yes. Deductible payments and coinsurance both count toward the out-of-pocket maximum. Once you hit that cap, the insurer pays 100% of further allowed costs.
- Do I still pay coinsurance before meeting my deductible?
- No. You pay the full allowed cost until the deductible is met; coinsurance only applies to the amount of the bill above your remaining deductible.