Denial Code Decoder
CO-45 — Charge exceeds the contracted rate
The billed amount is higher than the payer's fee schedule or your contracted rate, so the difference was adjusted off. On an in-network claim this is the ordinary contractual write-off — but a pattern of large CO-45 adjustments can hide an underpayment or a stale chargemaster.
Billable to the patient? No — a contractual adjustment is never billable to the patient on an in-network claim.
Where this denial is born
- Front desk
- Coding
- Claim build
- Submission
- Adjudication
This denial is usually created at the highlighted stage — that is where prevention lives.
Answer the questions — follow the path
The same questions an experienced biller asks, in order. Your answers draw the route to the right action.
Does the paid amount match your contracted rate for this code?
Compare the allowed amount on the remittance against the fee schedule in your contract.
The full decision tree
Does the paid amount match your contracted rate for this code?
Compare the allowed amount on the remittance against the fee schedule in your contract.
- Yes →
Post the contractual adjustment. This is the normal in-network write-off. Post it to the contractual adjustment bucket — not to patient responsibility.
- No →
Is the payment below the contracted rate?
If the allowed amount itself is wrong, this is an underpayment, not an adjustment.
- Yes →
Dispute the underpayment. Send the payer a payment dispute citing the contract rate and the remittance. Track it like an appeal, with the payer's dispute deadline on a clock.
- No →
Review the charge amount. If the payer allowed more than you expected, your fee schedule on file may be stale — verify the contract version before concluding anything.
- Yes →
Prevention
Load payer fee schedules into your system and run an allowed-vs-paid comparison on posting, so underpayments surface instead of disappearing into write-offs.
Related reading
The code list, and when it was last checked
X12 maintains the Claim Adjustment Reason Codes list, where this code is listed as 45. The list carries the number alone: the CO in front of it is the adjustment group the payer chose for this line, which decides who owes the balance, and the same code can arrive under a different group from a different payer. It has been on the list since January 1, 1995, and X12 last revised its entry on July 1, 2017.
Checked against the list revision dated November 1, 2025 on August 7, 2026, where it reads as an active code.
Sources
The paragraphs behind the guidance above. A page that tells you what to do about money should show you what the instruction rests on.
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