CO-29 Denial Code: The Time Limit for Filing Has Expired
CO-29 means the time limit for filing has expired — the claim arrived after the payer's timely filing deadline. Medicare allows 12 months from the date of service; commercial limits commonly run 90 to 180 days. It is appealable only with proof of timely original submission or a qualifying exception.
- Group
- CO — Contractual Obligation
- Category
- Administrative / timely filing
- Appealable?
- Yes — with proof of timely filing or a valid exception
- Typical fix
- Appeal with clearinghouse acceptance report; otherwise write off
What does denial code CO-29 mean?
Official X12 text: "The time limit for filing has expired." The payer received the claim after its filing deadline and refused to adjudicate it. Medicare's limit is 12 months from the date of service; Medicaid and commercial plans set their own, commonly 90, 120, or 180 days — check yours in the timely filing limits table.
Full guide: CO-29 denial code — complete walkthrough covers exception categories, evidence standards, and payer-by-payer appeal addresses. This card is the quick reference.
Why does CO-29 happen?
- Rejected claims nobody worked — the original submission bounced at the clearinghouse and sat unnoticed until the window closed.
- COB surprises — the claim went to the wrong primary payer first; by the time coordination of benefits was sorted, the correct payer's clock had run out.
- Held charges — encounters stuck in provider documentation or coding queues for months.
Mini-example: a $310 procedure claim rejects on day 5 for a bad subscriber ID, sits in an unworked rejection report, and is resubmitted on day 112 of a 90-day limit. Denied CO-29. Because the practice kept its original acceptance report showing the day-5 submission, the appeal was overturned in three weeks.
How do you appeal a CO-29?
- Locate proof of the original timely submission — clearinghouse acceptance report, 277CA, or payer claim number.
- Check your appeal window with the appeal deadline calculator; timely filing appeals have their own deadline.
- Send a short appeal: date of service, filing limit, original submission date, evidence attached. The appeal letter generator has a timely-filing template.
- No proof and no exception? Write it off and fix the process — do not rebill, which just generates a duplicate denial.
How do you prevent CO-29?
Work clearinghouse rejections daily — they are invisible on ERAs and are the top source of silent timely-filing deaths. Set your aging report to flag unbilled or unresolved claims at half the shortest filing limit you hold.
Frequently asked questions
Yes, if you can prove the claim was originally submitted in time. A clearinghouse acceptance report showing payer receipt within the limit is the gold-standard evidence. Other winning grounds: wrong payer information given by the patient, retroactive eligibility, or the payer's own misdirection — all documented in writing.
No. Timely filing is the provider's contractual duty, so the CO group applies and the balance is a write-off. Billing the patient for your own late filing violates network contracts and, for Medicare and Medicaid, program rules.
Documentation that the payer received the claim within the limit: the clearinghouse 277CA or acceptance report with date, payer claim number from the original submission, or a certified-mail receipt for paper claims. A screenshot of your PM system showing a "billed" date is usually rejected — payers want evidence of receipt, not transmission.
Sources & further reading
Reviewed by the ImmediCare Solutions RCM team
Certified billers and coders handling claims across 50+ specialties nationwide. This entry is reviewed against current payer policy and CMS rules. Last review: Jul 5, 2026.
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