CO-29 Denial Code: Timely Filing Limit Expired

What Does CO-29 Mean?

CO-29 means the claim arrived after the payer's filing deadline — the window between the date of service and the date the payer must receive the claim. Each payer sets its own limit: Medicare allows 12 months, many commercial plans allow only 90 or 180 days, and some Medicaid plans as little as 90 days.

Code group: CO (Contractual Obligation) · Appealable: Yes, with proof of timely submission or payer-caused delay. Without proof, it is a write-off — not billable to the patient.

Why CO-29 Happens

The claim genuinely sat unbilled — missed charge entry, a held encounter awaiting documentation, or a credentialing gap that paused billing.
The claim was submitted on time but rejected at the clearinghouse level and nobody worked the rejection, so the payer never 'received' it.
COB or eligibility confusion delayed billing the correct payer until after the primary's deadline passed.
The payer's received-date records are wrong — it happens, and it is provable.

How to Fix a CO-29 Denial — Step by Step

Pull your proof of timely submission: clearinghouse acceptance reports showing the payer accepted the claim within the window are the gold standard.

If you have proof, appeal — timely filing denials with acceptance reports attached are among the most winnable appeals in billing.

If the delay was caused by the payer (wrong COB file, retro-eligibility, credentialing backdating), cite the payer-caused delay; most contracts and many state laws grant exceptions.

If the claim truly missed the window with no defense, write it off — and importantly, you cannot bill the patient for a timely filing write-off.

Fix the leak: find out why the claim aged out and close that specific gap.

CO-29 Appeal Letter Template

Adapt this wording to your claim — replace the bracketed fields and attach the documentation it references:

This claim was denied under CO-29; however, our records demonstrate timely submission. Attached is the clearinghouse acceptance report showing the claim was received and accepted by [Payer] on [date], which is within the [X]-day filing requirement for the [DOS] date of service. We request the denial be reversed and the claim processed for payment.

How to Prevent CO-29

Work clearinghouse rejections daily — a rejected claim was never received by the payer.
Track claims by payer-specific filing deadlines with alerts at 30 and 15 days remaining.
Bill within 48–72 hours of the date of service as standard practice.

For the full breakdown of filing windows by payer type and every exception that still gets a late claim paid, see our timely filing limits guide.

Related Denial Codes

CO-16 — Missing information CO-22 — COB / other payer CO-109 — Wrong payer

← Back to the full denial code library

Reviewed by the LegitMedBilling denial management team. This guide is general billing information, not legal or payer-specific advice — always verify against your payer contract and current policy.

Frequently Asked Questions

Can we bill the patient when a claim denies for timely filing?

No. Timely filing is the provider's responsibility, and both payer contracts and CMS rules prohibit shifting that cost to the patient. CO-29 amounts are provider write-offs unless the denial is overturned.

What counts as proof of timely filing?

Clearinghouse acceptance reports (997/999/277CA showing payer acceptance), certified mail receipts for paper claims, or payer portal submission confirmations. A screenshot of your PM system showing you 'sent' the claim is usually not enough — you need evidence the payer received it.

The patient gave us the wrong insurance and the right payer's deadline passed. Any hope?

Often yes. Submit with the original payer's denial or eligibility documentation showing you billed the coverage you were given in good faith. Many payers grant exceptions when the delay was caused by incorrect member information, retro-eligibility, or COB updates.