What does CO-29 mean?

CO-29 is a Contractual Obligation (CO) denial: "The time limit for filing has expired." The claim was submitted after the payer's filing deadline, so it was denied for timeliness.

CO · Contractual ObligationCARC 29

Denial Code CO-29

Q: Is CO-29 the patient's responsibility or a provider write-off?

CO-29 carries the CO group code (Contractual Obligation): Provider/contractual responsibility — not billable to the patient while denied. A CO adjustment is the provider's responsibility, not the patient's: balance-billing the patient for a CO amount is a contract (and often compliance) violation. But CO does not automatically mean “write it off.” When the cause is fixable — missing information (CO-16), a modifier problem (CO-4), or NCCI bundling (CO-97) — you correct and resubmit, or appeal with documentation. You only truly write the amount off when it is a final contractual adjustment, such as the fee-schedule difference on CO-45.

The time limit for filing has expired.

Source: X12 Claim Adjustment Reason Codes (CARC) & Group Codes. Maintained by the D3rx Clinical Billing Team.

What CO-29 means

The claim was submitted after the payer's filing deadline, so it was denied for timeliness.

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CO group code: who absorbs the charge

Contractual Obligation — Provider/contractual responsibility — not billable to the patient while denied.

A CO adjustment is the provider's responsibility, not the patient's: balance-billing the patient for a CO amount is a contract (and often compliance) violation. But CO does not automatically mean “write it off.” When the cause is fixable — missing information (CO-16), a modifier problem (CO-4), or NCCI bundling (CO-97) — you correct and resubmit, or appeal with documentation. You only truly write the amount off when it is a final contractual adjustment, such as the fee-schedule difference on CO-45.

Why CO-29 happens

The claim sat unsubmitted past the timely-filing window
A resubmission after an earlier denial took too long to go back out
A lost original claim was rebilled past the deadline with no proof of the first attempt
A secondary claim was filed too late after the primary EOB was received

What to do when you get CO-29

1Look up the payer's exact timely-filing limit (Medicare 12 months; commercial commonly 90-180 days)
2Search for proof of timely original submission — clearinghouse acceptance reports, EDI acknowledgments, fax confirmations
3If you have proof, appeal with that documentation attached
4If there is no proof and the deadline truly passed, the charge is generally unrecoverable — adjust it off

Appeal, correct, or write off CO-29?

CO-29 is one of the few denials where an appeal (not a corrected claim) is the right path — but only if you can prove the claim was originally submitted on time. The deciding evidence is a clearinghouse acceptance report or EDI acknowledgment dated within the window; a corrected resubmission alone will just be denied again for timeliness. Without proof of timely original filing, most payers will not overturn CO-29.

Timing & deadlines

File the timely-filing appeal/reconsideration as soon as the denial posts — appeal windows are short (Medicare 120 days from the remittance; commercial often ~90-180 days). Prevention hinges on the initial limit: Medicare 12 months from date of service, most commercial payers 90-180 days.

Example

A claim is denied, corrected, and set aside; by the time it is resubmitted, 200 days have passed and the commercial payer's limit was 180. The resubmission is denied CO-29. Because the practice has a clearinghouse report showing the original claim was accepted on day 30, it appeals with that report and the payer reprocesses.

Prevent CO-29 going forward

Work an unsubmitted/held-claims report at least weekly
Track each payer's filing limit in your PM system and alert before it lapses
Retain clearinghouse acceptance reports as proof of timely filing
Resubmit corrected claims promptly rather than letting them age

Code families most affected

Any service, but especially aged AR and secondary claims
Claims that bounced once and were slow to resubmit
Coordination-of-benefits claims awaiting a primary EOB

Related codes

Denial codes you'll often see alongside CO-29

CO-16 CO-22 OA-23

Payer notes

Timely-filing limits are payer-specific and stated in the provider manual; the standard anchors are Medicare's 12-month initial limit and ~90-180 days for many commercial payers. Some payers grant exceptions for documented COB delays or proof of original timely submission, but the burden of proof is on the provider.

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Medical billing disclaimer

CARC/RARC definitions are the standardized X12 set; group-code semantics follow the X12 Claim Adjustment Group Code standard. Filing and appeal windows vary by payer — the standard anchors shown (Medicare redetermination 120 days from the remittance; Medicare timely filing 12 months from date of service; most commercial payers ~90-180 days) are general references, not a guarantee for any specific plan. Always confirm the rule in the payer's provider manual before acting. D3rx is not responsible for claim outcomes.