What does CO-45 mean?

CO-45 means the billed charge exceeded the allowed amount under your contract or fee schedule, so the difference is written off. CO is a contractual obligation, so it cannot be billed to the patient. It's the most common adjustment code.

Can you appeal a CO-45 adjustment?

The CO-45 write-off itself isn't appealable; it's the expected contractual adjustment. But you can and should dispute the allowed amount when it's lower than your contracted rate, which is a recoverable underpayment.

What is the difference between CO-45 and CO-97?

Both are contractual write-offs. CO-45 means the charge exceeded the allowed price (a pricing issue); CO-97 means the service was bundled into another already-paid service (a bundling issue).

Can I bill the patient for CO-45?

No. CO is a contractual obligation, so the CO-45 difference is a write-off you cannot pass on to the patient.

CO-45 Denial Code: Why It Hides Underpayments

CO-45is the most common code on any remittance, and the most ignored. It means “charge exceeds the fee schedule / maximum allowable or contracted amount.” Most of the time it’s routine and correct. But CO-45 is also where underpayments hide in plain sight, so it’s worth understanding exactly when to let it go and when to fight it.

What CO-45 means

CO stands for Contractual Obligation. The adjustment is governed by your payer contract and cannot be billed to the patient.
45 means the billed charge exceeded the allowed amount, so the difference is written off.

Example: you bill $200, your contract allows $120, the payer pays $120 and posts an $80 CO-45 adjustment. That $80 isn’t a denial. It’s the expected contractual write-off. This is normal and not appealable.

The trap: when CO-45 hides an underpayment

Here’s the catch. CO-45 only tells you the charge exceeded the allowed amount. It says nothing about whether that allowed amount was correct. If the payer’s allowed amount is lower than the rate in your contract, you’ve been underpaid, and it’s disguised as a routine CO-45 adjustment that nobody questions.

A normal-looking CO-45 with a wrong allowed amount is one of the highest-value leaks in a practice, because it’s systematic: the same payer underpricing the same code, claim after claim, with no one disputing it.

How to know which CO-45 to fight

Keep your contracted rates loadable. You can only spot an underpayment if you know what you were owed per CPT/HCPCS.
Compare allowed vs. contracted on every line. If allowed is below contracted, that delta is recoverable. Dispute it as an underpayment, not as a denial appeal.
Watch for downcoding.If the payer paid a lower-level code than billed and wrapped the difference in CO-45, that’s a separate, challengeable problem.
Let the rest go.When the allowed amount matches your contract, CO-45 is exactly what it should be. Don’t waste effort appealing a correct adjustment.

CO-45 vs. CO-97

Both are contractual write-offs, but for different reasons. CO-97 means a service was bundled into another already-paid service. CO-45 means the charge exceeded the allowed price. One is a bundling question; the other is a pricing question.

A note for Texas practices

Underpayments below your contracted rate are recoverable, and when a payer corrects one late, Texas prompt-pay provisions may add statutory interest. A CO-45 that masks an underpriced claim isn’t just lost principal; it can carry interest too.

The bottom line

CO-45 itself isn’t appealable. It’s the contractual adjustment working as designed. The recoverable money is in the allowed amountsitting next to it. Audit those numbers against your contract and you’ll separate the routine write-offs from the silent underpayments. See the revenue-leakage guide for the full picture.

CO-45 Denial Code: The Adjustment That Hides Underpayments