CO-131 denial code
A claim-specific negotiated discount was applied — a rate agreed for this claim rather than by your standing contract. Fine when you actually negotiated one. The reason to read this page: sometimes you didn't, and the discount is riding on an agreement you never signed.
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
- 1A single-case agreement you negotiated for an out-of-network patient, applied as agreed.
- 2A third-party repricer or rental-network discount applied to an out-of-network claim — sometimes with authority, sometimes on the strength of a network you never joined.
- 3A prompt-pay or settlement arrangement showing up as a line-level discount.
How do I fix a CO-131 denial?
- Match the discount to a document. If there is a single-case agreement, check the remit against its terms and hold the payer to them.
- If no agreement authorizes it, ask the payer in writing for the contractual basis of the discount. A discount with no contract behind it is disputable, and worth disputing.
- Post correctly either way — an agreed discount is a write-off; an unauthorized one is short payment.
Writing the appeal?
Our free generator drafts a CO-131 appeal letter that opens with the argument above — it runs entirely in your browser, so the claim details never leave your screen. No signup.
Generate the appeal letterHow to stop the next one
Keep single-case agreements where billing can see them, and reconcile OON payments against what was actually agreed rather than what arrived. Unauthorized discounts count on nobody checking.
Our diagnosis scrubber will not catch this one. CO-131 is driven by procedure codes, modifiers, or eligibility rather than by the diagnosis set — and procedure-side checking needs CPT codes, which aren’t included 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.