CO-29 means the payer received the claim after its filing deadline. Most CO-29 denials are permanent write-offs. The exceptions are when you can prove you filed on time, or when the delay qualifies for a documented exception. Everything else is a process fix.
1. What CO-29 means
- CO (Contractual Obligation): the provider absorbs it. You cannot bill the patient for your late filing.
- 29: the time limit for filing has expired.
Deadlines vary widely: 12 months for Original Medicare, and often 90 to 180 days for commercial contracts. Our timely filing limits by payer guide has the details.
2. When a CO-29 appeal can win
| Situation | Worth appealing? |
|---|---|
| You have a clearinghouse or payer acceptance report dated before the deadline | Yes |
| The payer received an earlier version of the claim on time and denied or rejected it for another reason | Often, with the original claim history |
| Retroactive eligibility or a payer error delayed billing | Sometimes, if the payer recognizes the exception |
| The claim simply went out late | No. Write it off and fix the cause. |
3. What counts as proof
- Clearinghouse acceptance reports showing the payer accepted the claim on a specific date (for example the 277CA acknowledgment).
- Payer acknowledgments or claim status responses showing receipt.
- Earlier remittances or letters about the same claim, dated before the deadline.
A note saying "sent" in your billing system is weak evidence. Store acceptance reports by claim so they are easy to find.
4. Find the root cause
- Charge lag: charges entered days or weeks after the visit.
- Rejections nobody worked: a rejected claim usually does not count as filed, so the deadline keeps running.
- Secondary claims never sent after the primary paid.
- Claims stuck in a hold queue waiting on information.
- Wrong payer billed first, with the right payer billed too late. See CO-109.
5. How to prevent CO-29
- Show days left to file on every claim in every work queue.
- Work rejections daily.
- Measure charge lag weekly, by provider.
- Sort aged AR by deadline, not just age. See our days in AR guide.
Related: CO-16, denial recovery playbook, and the full CARC and RARC codes list.
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