CO-29
CO · Contractual Obligation
CO-29 Denial Code: Filed past the timely-filing deadline
The claim was received after the payer's filing deadline. The amount is a contractual write-off unless you can prove timely submission or a valid exception.
- Group code
- CO - Contractual Obligation
- Code type
- CARC
- Billable to patient?
- No - contractual write-off
- Appealable?
- Only with proof of timely filing
- Category
- Timely Filing
- Common pairing
- N211
On a remittance
CAS*CO*29*125.00On a paper EOB it shows as CO-29.What CO-29 means
CO-29 is a timely-filing denial: the claim arrived after the payer's filing window (which varies widely by payer and contract). As a CO adjustment it cannot be billed to the patient. It is recoverable only when you can document timely original submission or a qualifying exception (such as retroactive eligibility or proof the delay was the payer's); for Medicare, pursue a reopening rather than a standard appeal.
Common causes
- The claim was genuinely submitted after the deadline.
- An original timely claim was rejected at the clearinghouse and never actually reached the payer.
- The claim bounced between payers due to a COB or wrong-payer issue, consuming the filing window.
- Retroactive eligibility or another circumstance delayed billing.
How to fix it
- Pull proof of timely submission: clearinghouse acceptance reports, payer acknowledgments, or submission logs.
- Appeal with that proof and reference the payer's timely-filing policy and any exception that applies.
- If a clearinghouse rejection caused the gap, include the original acceptance/rejection trail.
- If genuinely late with no exception, post the contractual write-off.
How to prevent it
- Submit claims daily and monitor clearinghouse acceptance reports - do not assume submitted means accepted.
- Work rejections immediately so a rejected claim does not silently miss the window.
- Track each payer's filing deadline and build aging alerts well before it.
Appeal potential
Only with proof of timely filingWinnable only if you can document the original claim was filed on time - the clearinghouse acceptance report is your best evidence. For Medicare this is a clerical reopening, not a standard appeal; RARC N211 signals a final determination the provider cannot appeal, so pursue a reopening with your timely-filing proof rather than an appeal.
Appeal letter template
Fill in the bracketed fields, attach your supporting documentation, and send through the payer's appeal channel. This is a starting point — adjust to your payer's requirements.
Re: Timely Filing Appeal (CO-29) - Claim [Claim Number] Patient: [Patient Name] | Member ID: [Member ID] Date(s) of Service: [DOS] To Whom It May Concern: Claim [Claim Number] was denied under CO-29 for timely filing. The claim was originally submitted on [Original Submission Date], within your [X]-day filing limit. Enclosed is the clearinghouse acceptance report / payer acknowledgment (reference [Ref Number]) confirming timely receipt. We request that the timely-filing denial be overturned and the claim processed on its merits. Sincerely, [Your Name], [Practice Name] | [Phone] | [NPI/TIN]