The CO-29 Denial: How to Overturn "Timely Filing" Rejections

The CO-29 denial ("Time limit for filing has expired") is the most common reason for write-offs. Learn how to use Clearinghouse logs to prove timely filing and recover this revenue.

CO-29

Of all the denial codes a biller sees on an Explanation of Benefits (EOB), CO-29 is the most frustrating.

The Definition: CO-29: The time limit for filing has expired.

Unlike a coding error (CO-11) or a medical necessity denial (CO-50), a CO-29 denial admits that you were right—you just weren't fast enough. For independent practices, this is a silent profit killer. It means the work was performed, the supplies were used, but the revenue is legally zero because a deadline was missed.

The "Hard" Deadlines

Every payer has a strict "Statute of Limitations" based on the Date of Service. If your billing team is backed up, these dates are the cliff where revenue dies.

• Medicare: 365 days (Strict).

• UnitedHealthcare & Cigna: Typically 90 days for network providers.

• Blue Cross: Varies by state, but often caps at 180 days.

  
  

Note: If you are seeing a spike in CO-29 denials, it is often a symptom of a backlog. Your team is prioritizing new, easy claims while the older, complex ones age out.

How to Fight the CO-29 Denial

Most billers write off CO-29 claims immediately because they believe they are impossible to win.

They are wrong.

You can overturn a CO-29 denial, but you cannot use a standard appeal letter. You must provide "Proof of Timely Filing" (POTF). You must prove that you attempted to send the claim within the window, even if the insurance company claims they "never received it."

The 3 Forms of Valid Proof:

1. The Clearinghouse Log (The Gold Standard): Don't just look at your EMR. Log into your clearinghouse (Availity, Waystar, Tellescope) and download the raw 277 acknowledgement report. Find the timestamp where the payer's gateway said "Accepted." This timestamp trumps their denial.

2. The EMR Audit Trail: A screenshot of your system showing the claim was generated and batched before the deadline. (Some payers reject this, but it is valid supporting evidence).

3. Certified Mail Receipt: If you submitted on paper, the USPS tracking number is your only defense.

The "Last Mile" Problem

Finding this proof takes time. Digging through clearinghouse logs for a single $120 office visit feels inefficient to an overworked billing manager. So, they skip it.

At L5 RCM, we call this the "Last Mile" problem.

Internal teams are built for volume (The First Mile). They are rarely staffed to fight the difficult, forensic battles required to overturn CO-29 denials (The Last Mile).

The Fix: Isolate the Problem

Don't force your current staff to stop billing new claims to fight old ones. That just creates a new backlog.

Instead, isolate your CO-29 denials into a separate bucket. Assign them to a Rescue Unit that specializes in forensic billing.

That is where L5 comes in. We don't replace your biller. We act as the rescue team that audits your CO-29 denials, locates the Proof of Timely Filing, and recovers the funds others write off.