The CO 45 denial code is on more remittances than any other code, and on most of them nothing has been denied: it is the payer saying the charge exceeds the fee schedule, the maximum allowable or the contracted rate, and the difference is the contractual adjustment the practice writes off. For the biller of a small practice, CO 45 is the code that has to be posted correctly rather than worked, because it is the line that turns a charge into an allowed amount. This page sets out what the code means, how the adjustment is posted against the claim, what the allowed amount says about the contract, and the cases where a CO 45 is a mistake rather than an adjustment.
What CO 45 means on the remittance
The payer allowed less than the charge, and the difference is a contractual obligation: an amount the provider agreed, in the participation contract or by accepting assignment, not to bill to the patient. X12 maintains the code as charge exceeds fee schedule, maximum allowable or contracted or legislated fee arrangement. On a paid claim the remittance shows the charge, the allowed amount, the CO 45 for the difference, and then how the allowed amount was split between the payer and the patient.
How the adjustment is posted against the claim
The CO 45 amount is posted as a contractual adjustment on the claim line, never as a patient balance and never as a bad debt. The free EOB reconciliation worksheet on this site works one line: the charge less the allowed amount is the adjustment, the allowed amount less the deductible and coinsurance is the payer payment, and the check line adds payment, patient share and adjustment back to the charge. A posting that does not balance to the charge has the CO 45 in the wrong place.
What the allowed amount says about the contract
The allowed amount behind a CO 45 is the contracted rate for that code with that payer, and across a month it is the practice's real fee schedule. A biller who records the allowed amount per code per payer on the register learns two things: which payers pay least for the practice's commonest codes, and when a payer's allowed amount changes without notice. The claims cycle worksheet here turns the month's adjustments into the net collection rate, which is the figure that separates a billing problem from a contract problem.
When a CO 45 is wrong
Sometimes the adjustment is the payer's error: the wrong fee schedule applied, an out-of-network rate on an in-network provider, a contracted rate missed after a renewal. The sign is an allowed amount well below the same code's allowed amount on last month's remittances from the same payer. That CO 45 is not posted and forgotten; it is appealed with the contract's rate sheet, and the register is where last month's allowed amounts are found.
Questions people ask about co 45 denial code
Is a CO 45 denial code a denial?
Usually not. It is the contractual adjustment on a paid claim, the part of the charge above the allowed amount. It is a denial only when the whole charge is adjusted and nothing is paid, which points at a coverage or contract problem.
Can I bill the patient for the CO 45 amount?
No. CO means a contractual obligation; the amount is written off under the participation contract. The patient owes only the deductible, coinsurance and copay the remittance applies.
Why is the CO 45 amount different for the same code from two payers?
Because each payer's contracted rate for that code is different. The allowed amount, not the charge, is what the practice is paid, and recording it per payer is how the practice learns its real fee schedule.
How do I know a CO 45 was applied at the wrong rate?
Compare the allowed amount with the same code's allowed amount on earlier remittances from that payer, and with the contract's rate sheet. A sudden drop is an appeal with the rate sheet attached.