CO-45 denial code
Your charge was above the payer's allowed amount, and the difference is a contractual write-off. This is not really a denial — it is the contract working exactly as written, and there is usually nothing to appeal.
CO — Contractual Obligation. The write-off is yours. You agreed to it in your contract with the payer, and you cannot bill the patient for it.
Why you got it
- 1Your fee schedule is set above the payer's allowed amount. That is normal and expected.
- 2The payer priced the service using a different fee schedule than you assumed.
- 3A pricing modifier changed the allowed amount.
How do I fix a CO-45 denial?
- Nothing, in most cases. Adjust the difference off as contractual. Billing the patient for it would breach your participation agreement.
- Do check the allowed amount is right. If the payer priced the service below the fee schedule you contracted at, that is worth disputing — but the dispute is about the rate, not the denial.
How to stop the next one
You cannot prevent CO-45 and should not try to. What you can do is know the allowed amount before you bill, so the write-off is expected rather than a surprise in the month-end numbers.
Our diagnosis scrubber will not catch this one. CO-45 is driven by procedure codes, modifiers, or eligibility rather than by the diagnosis set — and procedure-side checking needs an AMA CPT licence we do not hold yet. We would rather tell you that than sell you a tool that quietly misses your most common denial.
If denials like this are a volume problem rather than a one-off, the denial management page explains how the paid workspace catches the coding causes on every claim, and the free ICD-10-CM lookup shows the coding notes behind any diagnosis code on the remittance.