CO-45 on Your EOB: What It Means and What to Do

5 min read

Summary

CO-45 means the provider billed more than your plan's agreed price. The code starts with CO (Contractual Obligation), which usually means the provider must write off the difference. Most of the time you should not be billed for that amount.

What happened

Your Explanation of Benefits (EOB) shows the code CO-45. The official wording is: "Charge exceeds fee schedule/maximum allowable or contracted/legislated fee arrangement." In plain words, the provider billed more than the price your plan agreed to pay for that service.

What it means

The letters matter. CO stands for Contractual Obligation. It tells you the difference belongs to the provider under their contract with your plan. It is not your share.

For example, the provider bills $400. Your plan's allowed amount is $150. The $250 difference shows as CO-45 and gets written off. You may still owe your normal deductible, copay, or coinsurance, but only on the $150.

CO-45 is one of the most common codes. On its own it is not a denial of your care. It is a price adjustment.

Who handles this

The provider's billing office must apply the write-off to your account.
Your insurance plan set the allowed amount and can confirm the adjustment.
Your state insurance department can help if an in-network provider keeps billing you for the written-off amount.

What to do next

Find the line with CO-45 on your EOB. Note the billed amount, allowed amount, and "patient responsibility."
Compare it to the bill from the provider. The bill should match the patient responsibility, not the full charge.
If the bill is higher, call the billing office. Use the script below.
If they refuse, call your plan and ask them to contact the provider.
Keep notes: date, name, and reference number for every call.

Call script: provider billing office

"Hi, I'm calling about my account. My date of service was [date]. My EOB shows adjustment code CO-45, which is a contractual write-off. My patient responsibility on the EOB is [amount], but my bill shows [amount]. Can you apply the contractual adjustment and send me a corrected statement? Can I have your name and a reference number?"

Call script: your insurance plan

"Hi, I'm a member and I have a question about a claim from [date]. The EOB shows CO-45. The provider is billing me for the amount that was written off. Can you confirm the provider is in-network and that I should not be billed for the CO-45 amount? Can you contact the provider or give me a reference number I can share with them?"

When it is different

If the provider is out-of-network, the rules can differ. Some out-of-network providers may bill you the difference unless the federal No Surprises Act or your state law protects you (for example, emergency care or certain care at an in-network hospital). Call your plan to check.

Key takeaways

CO-45 means the charge was higher than your plan's allowed amount.
CO means Contractual Obligation: the provider usually writes off the difference.
You may still owe your deductible, copay, or coinsurance on the allowed amount.
An in-network provider generally should not bill you for the CO-45 amount.
Out-of-network care can follow different rules; check No Surprises Act protections.

Common questions

Is CO-45 a denial?

Not usually. It is a price adjustment. The service was processed, and the part above the allowed amount was written off.

Do I owe the CO-45 amount?

If the provider is in-network, generally no. Your share is what the EOB lists as patient responsibility.

What if the provider keeps billing me?

Ask your plan to contact the provider. If it continues, you can file a complaint with your state insurance department.

Should I appeal a CO-45?

Usually there is nothing to appeal. The fix is getting the provider to apply the write-off to your bill.

Helpful resources

X12 Claim Adjustment Reason Codes
The official list of adjustment codes and their exact wording.
CMS: No Surprises Act
Federal protections against certain surprise medical bills, plus a help line.
NAIC: Find your state insurance department
Where to file a complaint about a health plan or billing problem.

A verse for encouragement

“A false balance is an abomination to Yahweh, but accurate weights are his delight.”

— Proverbs 11:1

Scripture is offered for encouragement and reflection and is not a substitute for professional medical, legal, financial, or healthcare advice. Verses are quoted from the World English Bible, a public domain translation.

This article is educational information about how the healthcare system works. It is not medical, legal, or financial advice, and it does not describe any specific person’s case. Always confirm details with your insurer, your provider, or an official government source.