CO-226 denial code
The payer asked the billing provider for information and considers the answer missing, incomplete, or late. Somewhere there is a development letter with your name on it — the entire game is finding it and answering it properly.
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 records request went to an address or fax you stopped watching, and the response window expired quietly.
- 2Records were sent but incomplete — the request asked for three things and got two.
- 3The response was sent without the claim or request identifiers, so it never got matched to the claim it was meant to save.
- 4The response was simply late.
How do I fix a CO-226 denial?
- Find the original request. Call the payer if you have to — you need to know exactly what was asked and when the clock started.
- Send a complete response through the payer's stated channel, referencing the claim number and the request ID on every page.
- If you can show you never received the request — wrong address on their file, no delivery — appeal on that basis and get your correspondence address corrected while you are at it.
Writing the appeal?
Our free generator drafts a CO-226 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
Payer correspondence needs a work queue with deadlines, the same as denials do. A development letter aging in a mail tray is a denial with a countdown attached.
Our diagnosis scrubber will not catch this one. CO-226 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.