How to appeal a CO-29 timely filing denial

Can you appeal a timely filing denial?

It depends on who denied it. For Medicare, Claims Processing Manual chapter 1, section 70.4, says a denial for untimely filing is not an initial determination and is not subject to appeal. Section 70.6 says no formal appeal channel exists for a provider, though the contractor may informally review its decision at the provider's request.

For commercial and Medicaid plans, the limit and the dispute route come from the contract or the state, so the answer is in the payer's manual. The code write-up, with all four Medicare exceptions, is on the CO-29 code page. This post is the order of work.

Step 1: Is the denial actually correct?

Count the days yourself before you build anything. Payers do mis-date claims, and a wrong receipt date is the easiest denial to reverse.

A date can also look late for a reason that has nothing to do with you: the payer counted a resubmission, not the first claim, or it never matched the first claim to the patient.

Step 2: What proof of timely filing do I need?

Proof is a dated record that the payer, or another payer, accepted the claim inside the limit. A rejection is not proof, because a rejected claim never entered adjudication. For Medicare, section 70.3 says the receipt date becomes permanent only after a submission passes the completeness and validity edits.

• The clearinghouse acceptance report for the first submission, showing the batch date and the claim.
• The 999 and 277CA acknowledgments. The 999 reports the file, and the 277CA reports whether each claim was accepted or rejected.
• A payer portal screen or status response that shows the claim on file, with the date it was captured.
• For a secondary claim, the primary payer's EOB or denial, because some secondary payers start the clock there.
• Any letter or EOB from another carrier, and any dated rejection letter, if the payer's manual lists them as proof.

UnitedHealthcare's 2026 Administrative Guide, for example, lists the date submitted, the date accepted, member identification, date of service and provider identification as the content of proof, and it says another plan's date stamp is not a valid received date. Read your own payer's list. Medicare's A/B MACs and CEDI may purge a 999 from a submitter mailbox after five business days (chapter 24, section 50.3.3), which is why you save acknowledgments when the claim goes out.

Step 3: Which Medicare exception request fits?

If the claim is late and nothing in the payer's records helps, test the exceptions in 42 CFR 424.44(b). Each needs different evidence, and the request goes to the Medicare contractor.

The extension runs to the last day of the sixth calendar month after the month you were told of the correction or entitlement, and requests under the error exception made more than 4 years after the date of service get no extension. The Medicaid and Medicare Advantage recoupment exceptions are on the CO-29 page.

Section 70.6 adds a mechanical step. A provider that accepts responsibility for the late filing should file a no-payment claim. If you believe the beneficiary is responsible, you contact the contractor, file a no-payment claim and explain the circumstances in the remarks field. Section 70.4 adds that when the provider is responsible for the late claim, it may not charge the beneficiary beyond the deductible and coinsurance that would have applied.

Step 4: What goes in the request?

Keep it to one page and a stack of exhibits. The reviewer wants to see the dates in a row, not a story.

1. Identifiers: patient name, member ID, claim number, date of service, billed amount and your NPI.
2. The rule or contract term you rely on, quoted by number, such as 42 CFR 424.44(b)(1).
3. A dated timeline of every submission and response.
4. The exhibits, numbered, in the same order as the timeline.
5. The outcome you want: reprocess the claim under the original received date, or grant the extension.

What do I do when the exception does not apply?

Write it off as a CO-29 adjustment and do not bill the patient for it. Then find the cause, because a CO-29 is almost always a process failure rather than a coding one.

• Look for charges that sat unbilled. A long gap between the date of service and charge entry eats the window.
• Check the rejection queue. Claims rejected at the clearinghouse and never fixed are the most common source.
• Check payer matching. Medicare treats a claim sent to the wrong contractor as not filed until the right one receives it, and the CO-109 page covers the wrong-payer denial.
• Set a work-by date well inside the limit, so A/R follow-up starts with time to spare.

How Nucleus Align handles filing deadlines

We send claims within 24 hours of charge entry and work denials within 48 hours, so a filing limit seldom becomes the problem. When a CO-29 does arrive, our denial management team pulls the first accepted date from the clearinghouse and the payer record. See also the denial management playbook. Book a call to talk through a batch of late claims, or read more on the blog.