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.
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]