CO-29 on a dental claim: timely filing denials, and the rare cases you can win
CO-29: The time limit for filing has expired. What it means on a dental claim, why dental offices get it, what to do, and whether the patient owes it.
By Dr. Salem Sayegh, general dentist, Glendora, California ·
The short answer: CO-29 means the claim reached the payer after its filing deadline. Dental plans set their own limits, commonly somewhere between 90 days and a year from the date of service, so check each payer’s provider manual. You can win an appeal only with proof that the claim was filed on time; otherwise an in-network office absorbs the amount.
| Code | CO-29 (adjustment reason code) |
|---|---|
| Group | CO, contractual obligation: the office absorbs it |
| Meaning | Filed after the payer’s deadline |
| Is it a denial? | Yes |
| Bill the patient? | No, when in network |
| Usually fixable? | Only with proof of timely filing |
Why dental offices get CO-29
- Claims that sat unsent, often after a staff change or during a posting backlog.
- A claim rejected at the clearinghouse that nobody noticed, so the original was never received.
- A CO-16 or CO-252 that was never corrected and resubmitted.
- Secondary claims sent long after the primary paid.
What to do about CO-29
- Look for proof of timely filing: a clearinghouse acceptance report, a payer acknowledgment, or a dated portal submission.
- If you have it, appeal with that proof and ask the payer to reprocess.
- If you do not, post the amount as a write-off under your contract.
- Find out why the claim was late, and fix that step so it does not happen again. Unworked rejections are the usual cause.
Can you bill the patient for CO-29?
No, for an in-network office. A missed filing deadline is the office’s responsibility under most PPO contracts, so the amount is not billable to the patient.
Questions about a specific EOB line?
Ask Sai Biller, our free dental insurance chatbot. Type the codes and amounts from the line, leave out patient details, and it explains what happened and what to do next. For offices posting every day, Sai for Dentists reads each EOB line as it posts, checks the allowed amount against your contracted fee and lists every denial, downgrade and underpayment for your team.
Sources
- X12 claim adjustment reason codes and remittance advice remark codes. Meanings here are paraphrased; see X12 for the official wording.
- American Dental Association, CDT: Code on Dental Procedures and Nomenclature. Procedure labels here are our own short descriptions.
- Payers apply these codes differently. Your contract and each payer’s provider manual decide what applies to your office.
Common questions
What is the timely filing limit for dental claims?
It varies by payer and plan. Limits commonly range from 90 days to a year from the date of service, and secondary claims may have their own limit from the primary payment date. Check each payer’s provider manual or your contract.
What counts as proof of timely filing?
A clearinghouse report showing the payer accepted the claim, a payer acknowledgment (such as a 277 response), or a dated portal submission confirmation. A copy of the claim from your own software is usually not enough by itself.
Can a posting backlog cause CO-29 denials?
Yes. When EOBs are not posted, rejections and requests for information go unnoticed, so claims that need to be resubmitted miss the deadline.
