What does denial code CO-29 mean?

CO-29 means the claim was received after the payer's timely filing deadline and will not be considered on the merits. It is a contractual adjustment that cannot be billed to the patient.

Can a CO-29 timely filing denial be appealed?

Yes, but it succeeds only with proof the claim reached the payer inside the window - typically a clearinghouse 277CA acknowledgement - or a documented exception such as retroactive eligibility or a coordination-of-benefits delay. Appeal deadlines for CO-29 are separate from and often shorter than the filing window itself.

Can I bill the patient after a CO-29 denial?

No. The delay was the provider's, so the write-off is contractual. Balance-billing a patient for a late-filed claim violates most payer contracts and is restricted by law in many states.

CO-29: The time limit for filing has expired

CO-29 is the most expensive routine denial in revenue cycle because it is almost never overturned. The service was likely payable; the claim simply arrived late. Every payer sets its own filing window - anywhere from 90 days to a full year from the date of service - and the clock usually starts at the date of service, not the date you learned about the coverage. The only reliable defense is proof the claim was submitted on time.

What it means: The claim reached the payer after its timely filing deadline, so it will not be adjudicated on the merits.
Who pays the balance: Contractual - and specifically one you cannot pass to the patient, because the delay was the provider's.
Group code CO: Contractual Obligation - the provider absorbs the balance and cannot bill the patient

Why CO-29 happens

The claim sat in a scrubber or clearinghouse rejection queue that nobody worked, so it never reached the payer at all.
Coverage was discovered late - the patient presented as self-pay and insurance surfaced months later.
A primary payer took months to adjudicate, pushing the secondary claim past its own window.
The claim was billed to the wrong payer and the correct one was identified after the deadline.
Credentialing was incomplete, so claims were held rather than submitted.

How to fix a CO-29 denial

1
Produce proof of timely submission
The clearinghouse acknowledgement (277CA) or the payer's own claim receipt showing a date inside the window is the only argument that reliably wins. A screenshot of your billing system is generally not accepted, because it proves you created the claim, not that the payer received it.
2
Check whether an exception applies
Most payers waive the limit for retroactive eligibility, for coordination-of-benefits delays where the primary's EOB date starts a fresh window, and for administrative errors by the payer. Cite the exception by name from the payer's provider manual.
3
Appeal within the appeal window, which is separate
The deadline to appeal a CO-29 is its own clock and is often shorter than the filing window that was missed. Missing it forecloses the appeal entirely.
4
If it cannot be overturned, write it off correctly
Adjust it as a contractual write-off, not patient responsibility. Balance-billing a patient for your own late filing is prohibited under most contracts and, in many states, by law.

Deadlines depend on the payer

Filing limits and appeal windows for CO-29 vary by payer and often by plan type within the same payer. Look up the specific payer to see its verified deadlines and the source document they came from.

Browse payer billing references

Preventing CO-29 denials

Work clearinghouse rejection queues daily - claims sitting in rejection have not been filed, regardless of what the billing system says.
Track each payer's filing limit as a hard field and age claims against that payer's specific deadline rather than a single global threshold.
Submit secondary claims as soon as the primary remittance posts rather than batching them.

CO-29 frequently asked questions

What does denial code CO-29 mean?: CO-29 means the claim was received after the payer's timely filing deadline and will not be considered on the merits. It is a contractual adjustment that cannot be billed to the patient.
Can a CO-29 timely filing denial be appealed?: Yes, but it succeeds only with proof the claim reached the payer inside the window - typically a clearinghouse 277CA acknowledgement - or a documented exception such as retroactive eligibility or a coordination-of-benefits delay. Appeal deadlines for CO-29 are separate from and often shorter than the filing window itself.
Can I bill the patient after a CO-29 denial?: No. The delay was the provider's, so the write-off is contractual. Balance-billing a patient for a late-filed claim violates most payer contracts and is restricted by law in many states.

Related denial codes

CO-16 CO-22 CO-109

Denial code explanations are original plain-English summaries written for reference and are not the official X12 code descriptions. Payer handling of any code varies by contract - always verify against the remittance advice and your payer agreement before adjusting a claim.