Coinsurance vs copay: what's the difference?
A copay is a fixed dollar amount you pay for a service — $30 for an office visit, say. Coinsurance is a percentage of the allowed amount — 20% of whatever your plan agreed the service costs. The key difference: a copay is predictable, while coinsurance depends on the negotiated price, so you often can't know it until the claim is processed.
How coinsurance is actually calculated
Coinsurance applies to the allowed amount, not the provider's list price. If a provider bills $1,000, your plan's allowed amount is $400, and your coinsurance is 20%, you owe $80 — not $200. Charging your percentage against the full list price is a real and costly error.
Where the deductible fits
Most plans apply your deductible first: until you've met it, you may owe the full allowed amount. After that, coinsurance kicks in and you split costs with the plan until you hit your out-of-pocket maximum, after which the plan generally covers the rest.
When it's worth questioning
- Your coinsurance was calculated on the billed amount instead of the allowed amount
- You were charged both a copay and coinsurance for the same service without explanation
- The percentage on your bill doesn't match your plan documents
- You're still being charged after hitting your out-of-pocket maximum
- A deductible was applied to a service your plan covers at 100%
Is it legit on your bill?
That's what it means in general. Fineprint reads your specific bill, flags the charges worth questioning, and drafts the letter for you — in about 60 seconds. Your first one is free.
Decode my bill freeFAQ
Do I pay coinsurance on the billed amount or the allowed amount?
The allowed amount. This is a common and expensive error — if your coinsurance was calculated against the provider's full list price, you're being overcharged, and it's worth questioning.
Can I owe both a copay and coinsurance?
Sometimes, depending on plan design and the type of service, but it's not typical for a single routine visit. If both appear, ask the billing department to explain each one.
Why was my coinsurance higher than I expected?
Usually because you hadn't met your deductible yet, the provider was out of network, or the allowed amount was higher than you assumed. Your EOB shows the math.
Related terms
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This is general information, not legal, medical, or financial advice. Rules and protections vary by state and situation. For a specific or high-stakes bill, consider consulting a professional.