CO-45 on a dental EOB: the in-network write-off, and when it hides an underpayment
CO-45: Charge exceeds the fee schedule or maximum allowable amount. What it means on a dental claim, why dental offices get it, what to do, and whether the patient owes it.
By Dr. Salem Sayegh, general dentist, Glendora, California ·
The short answer: CO-45 means your submitted fee is higher than the fee the payer allows under its fee schedule or your contract. For an in-network dental office it is the normal contractual write-off, not a denial: you adjust off the difference and cannot bill it to the patient. The thing to check is whether the allowed amount matches your contracted fee.
| Code | CO-45 (adjustment reason code) |
|---|---|
| Group | CO, contractual obligation: the office absorbs it |
| Meaning | Your fee is above the payer’s fee schedule or maximum allowable |
| Is it a denial? | No. It is the expected adjustment on almost every in-network line |
| Bill the patient? | No, not the CO-45 amount |
| Worth a second look when | The allowed amount is lower than the fee in your contract |
Why dental offices get CO-45
- Your office fee is above your contracted PPO fee, which is true of nearly every in-network claim.
- The payer applied a lower fee schedule than the one in your contract, such as an older year’s schedule or a different network’s.
- An alternate benefit clause paid a cheaper procedure’s fee, for example a posterior composite paid at the amalgam rate, and the payer reported the reduction under 45.
- The office is out of network and the payer applied its maximum allowable amount.
What CO-45 looks like on an EOB
| Procedure | Billed | Allowed | Paid | Adjustments |
|---|---|---|---|---|
| D2740 (porcelain crown) | $1,400.00 | $950.00 | $475.00 | CO-45 $450.00, PR-2 $475.00 |
The $450 CO-45 is written off. The patient owes the $475 coinsurance (50% of the $950 allowed). If your contract says $1,010 for D2740, the payer underpaid by $60 even though nothing on the EOB looks wrong.
What to do about CO-45
- Post the CO-45 amount as a contractual write-off, not as a patient balance.
- Compare the allowed amount with the contracted fee for that code and that payer. This is the step most offices skip.
- If the allowed amount is low, check whether the payer used the right fee schedule year and network, then ask for reprocessing with a copy of the contracted fee.
- If the line was downgraded under an alternate benefit, check your contract and your state’s rules on whether the patient owes the difference.
Can you bill the patient for CO-45?
No, not for the CO-45 amount itself. That is the discount you agreed to when you joined the network. The patient still owes any PR amounts on the same line, such as deductible or coinsurance.
Questions about a specific EOB line?
Ask Sai Biller, our free dental insurance chatbot. Type the codes and amounts from the line, leave out patient details, and it explains what happened and what to do next. For offices posting every day, Sai for Dentists reads each EOB line as it posts, checks the allowed amount against your contracted fee and lists every denial, downgrade and underpayment for your team.
Sources
- X12 claim adjustment reason codes and remittance advice remark codes. Meanings here are paraphrased; see X12 for the official wording.
- American Dental Association, CDT: Code on Dental Procedures and Nomenclature. Procedure labels here are our own short descriptions.
- Payers apply these codes differently. Your contract and each payer’s provider manual decide what applies to your office.
Common questions
Is CO-45 a denial?
No. CO-45 is a contractual adjustment that appears on almost every in-network dental claim. The line is usually paid; the code only explains why the allowed amount is below your fee.
Can I bill the patient for a CO-45 adjustment?
Not as an in-network provider. The CO group means the amount is the office’s contractual obligation. Billing it to the patient is balance billing, which most PPO contracts prohibit.
How do I know if CO-45 is hiding an underpayment?
Compare the allowed amount on each line with the contracted fee for that procedure code. If the allowed amount is lower, the payer used the wrong fee schedule or made an error, and the EOB will still just say CO-45.
