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. Payer-by-payer: filing limits and exceptions
| Payer | What to know |
|---|---|
| Medicare | Claims must be filed within 12 months of the date of service. Exceptions exist for Medicare administrative error, retroactive Medicare entitlement, and retroactive disenrollment from Medicare Advantage. If one applies, cite it in the reopening or appeal. |
| Medicaid | Federal rules require most claims within 12 months of service, but states set their own, often shorter, limits. When Medicaid is secondary, the clock usually runs from the primary payer's remittance date, so keep that remittance. |
| Commercial plans | Limits come from your contract and state law, commonly 90 to 180 days for participating providers. Corrected claims and appeals often have their own, separate deadlines. See timely filing limits by payer. |
| TRICARE | Claims must be filed within one year of the date of service, or one year from the date of discharge for inpatient care. |
The proof that wins most often is the clearinghouse acceptance report (999 and 277CA) showing the payer received the claim before the deadline. A billing system note that says "submitted" is rarely enough.
6. 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.
Is your team working CO-29 denials manually?
We build the software that does the repetitive part of denial work: reading every remittance, sorting denials by cause, and drafting the correction or appeal for CO-29 and every other code. Your team approves before anything goes out.
Book a 20-minute look →Frequently asked questions
Tell us what your team does manually.
A 20-minute call. Tell us what your team does manually, from denials to posting to status checks, and we will tell you whether it is worth building. No slides.
Book a 20-minute look →