What Is Coinsurance
Coinsurance is the percentage of the allowed amount you pay for covered medical services after you've met your deductible. If your plan has 20% coinsurance, you pay 20% of what your insurance company has determined is the "allowed amount" for that service, and your insurer pays the remaining 80%.
The allowed amount is critical here. It's not what your provider charged, but what your insurance plan negotiated as reasonable for that procedure. Your EOB will show three figures: the provider's billed charge, the allowed amount, and what you owe based on your coinsurance percentage.
How Coinsurance Affects Claim Denials and Appeals
Many patients mistake coinsurance charges for claim denials. If your EOB shows you owe 20% coinsurance on an allowed amount of $1,000, you owe $200. That's not a denial, it's your cost share. However, insurers sometimes deny claims citing medical necessity, lack of prior authorization, or out-of-network status, and you'll see zero insurance payment. That's different from coinsurance, and it requires an appeal.
When filing an internal appeal, clarify whether the issue is coinsurance (a cost-sharing obligation) or coverage denial (a payment refusal). Your appeal strategy differs significantly. For a coverage denial, you'll cite medical necessity, treatment guidelines, or peer-reviewed evidence. For coinsurance disputes, you'd challenge whether the allowed amount was calculated correctly or whether the service should have been covered at a different percentage.
How Coinsurance Works With Your Deductible
- Deductible comes first: You pay 100% of covered services until you hit your deductible (often $500 to $2,500 per year).
- Coinsurance comes after: Once you've met the deductible, coinsurance kicks in. You typically pay 10% to 40% depending on your plan tier and service type.
- Out-of-pocket maximum matters: Your coinsurance and copay amounts count toward your out-of-pocket maximum. Once you hit that ceiling (often $7,000 to $15,000), your insurance covers 100% for the rest of the year.
Real Claim Example
You have a $1,500 deductible and 20% coinsurance. You have an MRI that your provider bills at $2,800. Your insurance's allowed amount is $1,200. First, you pay $1,200 toward your deductible (now met). The remaining services that year: you pay 20% coinsurance on allowed amounts. This is where prior authorization matters. If your MRI wasn't pre-authorized and your plan requires it, the claim could be denied entirely, and you might owe the provider's full billed charge unless you appeal within state-mandated timeframes (typically 30 days for internal appeals, 60 days for external appeals under most state insurance regulations).
Common Questions
- Why does my EOB show a higher charge than my coinsurance is based on? The allowed amount is what your insurance negotiated with the provider, not the billed charge. Coinsurance is calculated on the allowed amount only. The difference is often written off by the provider.
- Can I appeal a coinsurance amount? Yes, if you believe the allowed amount is incorrect or if the service should have required a copay instead. Request a recalculation and cite your plan documents. Most insurers respond within 30 days.
- Does coinsurance apply if I go out-of-network? Often your coinsurance is higher out-of-network, or the service isn't covered at all. Check your plan documents. Out-of-network denials are frequent appeal targets, especially if no in-network providers offered the service.