Coinsurance Calculator

What Coinsurance Actually Means

Coinsurance is the percentage of the allowed amount — not your billed charge, not your total bill — that you owe after your deductible has been met. If your plan is "80/20," the insurance company pays 80% of the allowed amount and you pay the remaining 20%, but only once your deductible is satisfied for the year. Before that, most plans require you to pay 100% of the allowed amount yourself, which is why the exact same office visit can cost you $400 in January and $37 in November, even though nothing about the visit or your coverage changed. This calculator handles both phases — deductible and coinsurance — in a single pass, and now also factors in a copay, multiple units of service, and your out-of-pocket maximum.

How to Read Your Result — A Worked Example

Say your plan is 80/20 with a $500 deductible and you've already paid $350 of it toward this year's care. A specialist visit and procedure comes back with a $600 allowed amount:

Plug those numbers into the calculator above (allowed amount $600, coinsurance rate 20%, deductible remaining $150) and you'll get the identical $240 / $360 split — that's exactly the math your insurer runs when the claim adjudicates.

Common Coinsurance Splits

The percentage varies by plan tier and network status. These are the splits you'll see most often on an Explanation of Benefits (EOB):

Coinsurance vs. Copay vs. Deductible

These three terms get used interchangeably by patients — and mixed up on statements when billing staff aren't careful. They're not the same thing:

• Deductible — the amount you pay in full before coinsurance starts. Resets every plan year. Reported on remittances as PR-1.
• Coinsurance — the percentage split that applies after the deductible is met. Reported as PR-2.
• Copay — a fixed dollar amount per visit type (e.g., $30 primary care, $60 specialist), usually charged independently of the deductible and coinsurance math. Reported as PR-3.

For billers: PR amounts are legitimately billable to the patient — unlike CO adjustments, which are provider write-offs the practice absorbs. Confusing a CO adjustment for a PR amount (or vice versa) on a patient statement is one of the fastest ways to create refund liabilities and patient complaints.

How the Out-of-Pocket Maximum Caps Your Coinsurance

Every ACA-compliant plan has an annual out-of-pocket maximum — the most you'll pay in deductible, copays, and coinsurance combined in a plan year. Once you hit it, the plan pays 100% of covered, in-network services for the rest of the year. That's what the "out-of-pocket max remaining" field above does: if your deductible-plus-coinsurance share on this claim would push you past what's left of your cap, the calculator stops your responsibility at the cap and shows the plan absorbing the difference — exactly how your insurer's adjudication system handles it.

Why the Allowed Amount, Not the Billed Charge, Sets Your Coinsurance

Providers in a payer's network agree by contract to accept a specific reimbursement rate for each service — the allowed amount — regardless of what the provider's standard charge (chargemaster rate) says. Coinsurance is always calculated against that contracted allowed amount, never the sticker-price charge. The gap between the two is a contractual write-off the provider absorbs, not something the patient owes. If a bill shows coinsurance calculated against the full billed charge instead of the allowed amount, that's a billing error worth flagging — see our CO-45 guide for how that adjustment is supposed to work on the provider side.