CO 29 denial code

What CO-29 means

CO-29 means the claim reached the payer after its filing deadline, so it was denied without any review of the service itself. The care may have been covered and correctly coded; the claim was simply too late.

For Medicare, the limit is 12 months from the date of service: claims must reach the MAC no later than one calendar year after the service date. Commercial and Medicaid limits vary widely, from 90 days to a year or more; check each payer’s contract.

The CO group code carries real weight here. Contractual obligation means the missed deadline is the provider’s problem: the balance is a write-off, and the patient cannot be billed for it. That makes CO-29 one of the most expensive denials in the book; there is usually no path to payment, only prevention.

Common causes

• Claims stuck in edit queues. A claim held for a coding question or missing information ages past the deadline while waiting for someone to work it.
• Front-end rejections never corrected. The clearinghouse rejected the claim on day 3; nobody saw the rejection report, and the claim was never truly filed.
• Payer ping-pong. The claim bounced between a primary and secondary payer (see CO-22) or was sent to the wrong payer entirely, and the correct payer’s window closed in the meantime.
• Late charge entry. Encounters documented weeks after the visit, or charges discovered in a reconciliation months later.
• Retroactive eligibility. The patient’s coverage was established after the service, sometimes after the window closed: one of the few scenarios with a real exception.

How to fix and resubmit

1. Establish the actual first-submission date. Pull clearinghouse acceptance reports and submission logs. If the claim was accepted by the payer inside the window and the denial is an error, submit proof of timely filing through the payer’s dispute process; this is the most winnable CO-29.
2. For Medicare, check whether a filing-limit exception applies. CMS recognizes a short list, including retroactive Medicare entitlement, retroactive disenrollment from a Medicare Advantage plan, and errors by Medicare or its contractor. If one fits, request it through your MAC with documentation; this runs through the exception/reopening process described in the Medicare Claims Processing Manual, not a standard redetermination.
3. For commercial payers, read the contract’s timely filing clause. Many honor proof of timely original submission; some allow exceptions for coordination-of-benefits delays if you show the primary’s remittance date.
4. Do not resubmit the same late claim hoping for a different result; it will deny again, and repeated submissions can also trigger duplicate denials (CO-18).
5. If no exception or proof exists, write it off, and record the root cause. A CO-29 write-off without a documented cause will repeat.

How to prevent it

Work rejection reports daily: a rejected claim is an unfiled claim, and rejections are where most timely filing losses begin. Set aging alerts well inside each payer’s limit (for Medicare, flag anything unbilled at 60 days and unresolved at 6 months). Enter charges within days of service, not billing cycles. Keep a payer-by-payer filing-limit table where follow-up staff can see it, and preserve clearinghouse acceptance reports for at least the length of your longest limit plus appeal window: they are your proof when a payer mislays a claim. More codes are covered in the denial codes index.