Timely Filing Denials (CO-29): How to Overturn Them

CO-29 — "The time limit for filing has expired" — is one of the most frustrating denial codes in medical billing. It feels like a closed door: the window has passed, the money is gone. In practice, it's often a recoverable denial — if you know what evidence to submit.

What CO-29 actually means

Every payer sets a timely filing deadline — the window after the date of service during which a claim must be received. Deadlines vary:

• Medicare: 12 months from the date of service
• Medicaid: varies by state — often 90 days to 12 months
• Commercial payers: typically 90–180 days, though some contracts allow up to 12 months
• Some contracts run from date of discharge rather than date of service

CO-29 fires when the payer received the claim after the deadline — or when their records show no claim at all before the deadline.

The three scenarios — and how each is handled

1. The claim was submitted on time but the payer has no record of it

This is the most recoverable scenario. Claims get lost in clearinghouse transmission, rejected without notice, or simply not received. Your clearinghouse acceptance report is proof the claim left your system before the deadline.

What to submit with your appeal:

• Clearinghouse acceptance report showing the claim was submitted and accepted before the filing deadline
• The original submission date and transaction/batch ID
• If the claim was mailed, certified mail receipts or tracking confirmation

2. The claim was submitted on time, rejected, and resubmitted late

This is one of the most common causes of CO-29. A claim is submitted timely, rejects for a minor error (wrong NPI, invalid code), gets corrected, and resubmitted — but the corrected submission lands after the deadline. Most payers have a policy that a timely original submission preserves filing rights even if a corrected claim comes in late.

What to submit:

• The original submission date and clearinghouse confirmation showing the timely initial filing
• The payer's rejection notice for the original claim
• The corrected resubmission with the correction date
• A written explanation of the sequence of events

3. The claim was genuinely filed late

If the original submission really did miss the deadline, recovery depends on whether an exception applies. Most payers allow exceptions for:

• Retroactive eligibility changes — if coverage was added retroactively after the filing deadline passed
• Administrative or payer error that caused the delay (e.g., the payer's portal was down)
• Coordination of benefits situations — secondary claims can't be filed until the primary has paid
• Mental incapacity, incarceration, or other circumstances beyond the provider's control (payer-specific)

How to write the CO-29 appeal letter

The appeal letter needs to do three things: (1) identify the specific exception that applies, (2) provide the documentary evidence, and (3) cite the payer's own timely filing exception policy. Most payers publish their exception criteria — find it and quote it directly.

A strong CO-29 appeal letter looks like this:

The most common mistake: not having the clearinghouse reports

The single most important habit to prevent and overturn CO-29 denials is saving clearinghouse acceptance reports for every submission. Without them, proving timely filing is nearly impossible. Most practice management systems and clearinghouses allow you to download or export submission logs — set up a retention policy if you don't have one.

For more on CO-29, see the CO-29 denial code reference.