What does denial code CO-29 mean?

CO-29 means the claim was submitted after the payer's timely filing deadline — the window of time after the date of service during which claims must be received. The only way to overturn a CO-29 is proof that the claim was actually submitted on time (clearinghouse acceptance report or payer acknowledgment). If the claim was genuinely filed late, the balance must be written off and cannot be billed to the patient.

Can I bill the patient for a CO-29 write-off?

No. CO-29 is a Group CO (Contractual Obligation) denial, meaning the balance is a provider write-off. The payer's contract prohibits you from billing the patient for services that were not billed to the payer within the required timeframe. The write-off is the provider's loss, not the patient's responsibility.

What proof does a payer accept for a timely filing appeal?

Most payers accept: (1) clearinghouse acceptance report showing the submission date and acknowledgment within the filing window; (2) 999 or 277CA acknowledgment from the payer or clearinghouse; (3) prior denial letter from the payer dated within the filing window (proving receipt); (4) certified mail receipt if submitted on paper. They do not accept internal PM system dates, charge entry dates, or your billing software's export date — what matters is when the payer received it, not when you sent it.

Does a prior denial restart the timely filing clock?

It depends on the payer and the reason for the prior denial. Many payers — including Medicare — allow a new timely filing window from the date of a prior denial when you are resubmitting a corrected claim. Medicare specifically grants a new timely filing period when the initial denial was for a reason other than timely filing (such as CO-22, CO-16, or CO-109). Always check the payer's specific timely filing policy in the provider manual or call provider services to confirm before writing off a claim where a prior denial exists.

What are typical timely filing deadlines by payer?

Medicare: 12 months from date of service. Medicaid: varies by state, typically 90–365 days. Commercial plans: 90–365 days, most commonly 90–180 days. TRICARE: 180 days from DOS (or from primary EOB date for secondaries). Workers' comp: varies by state, typically 1–3 years. Employer self-funded plans (ERISA): check the Summary Plan Description — ERISA doesn't specify a minimum, and some plans have 60-day windows. Always verify in the specific payer contract — your billed amount is irrelevant once the window closes.

What is the timely filing window when Medicare is secondary?

When Medicare is secondary, the timely filing clock typically runs from the date of the primary payer's Explanation of Benefits (EOB), not from the date of service. Medicare allows up to 12 months from the primary EOB date for secondary claims. This is a common area of confusion — if you waited for the primary to process and then submitted Medicare secondary late, you may still be within Medicare's window measured from the primary EOB date.

How do I prevent CO-29 denials?

Prevention requires a filing deadline work queue in your PM system. Every claim should be flagged with the payer's timely filing deadline at the time the claim is created. A daily work queue report should show all claims approaching their deadline that have not been filed (still in pending, hold, or not submitted status). Claims within 30 days of their deadline should be escalated. Track CO-29 volume by payer, by provider, and by charge entry staff to identify where lag is occurring — clinical charge lag is the most common root cause.

CO-29 Denial Code: Timely Filing Expired — Appeal

CO-29 in plain English

CO-29 means the claim arrived after the payer's filing deadline. If you have proof it was submitted on time (clearinghouse acceptance report, 999/277CA acknowledgment, or a prior denial dated within the window), you can appeal and win. If the claim was genuinely filed late, write it off — you cannot bill the patient. CO-29 is almost entirely preventable with filing deadline work queues in your PM system.

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CO-29 write-offs cannot be billed to the patient under any circumstances

CO is a Contractual Obligation group code — the provider bears the loss, not the patient. Billing a patient for a CO-29 denial is a contract violation and may constitute a HIPAA/CMS compliance issue. Write off the balance and document the root cause for internal process improvement.

Filing Deadlines by Payer Type

Timely filing windows — know these before any CO-29 lands

Always verify the exact window in the payer's provider manual or your contract. The table below reflects common defaults — individual contracts may differ.

Payer Type	Window	Clock Starts	Secondary Claim Rule
Medicare Part B	12 months	Date of service	12 months from primary EOB date
Medicare Part A (facility)	12 months	Date of service / discharge	12 months from primary EOB date
Medicaid	90–365 days (state-specific)	Date of service	Varies; often from primary EOB date
TRICARE	180 days	Date of service	180 days from primary EOB date
Commercial (most plans)	90–180 days	Date of service	Varies; often from primary EOB
Blue Cross / Blue Shield	180 days (most plans)	Date of service	180 days from primary EOB
UnitedHealthcare	90–180 days	Date of service	90 days from primary EOB
Aetna	180 days	Date of service	180 days from primary EOB
Cigna	180 days	Date of service	180 days from primary EOB
Workers' Compensation	1–3 years (state law)	Date of service / treatment authorization	State-specific
ERISA self-funded plans	60–90 days (plan document)	Date of service	Check SPD — no federal minimum
Marketplace / ACA plans	180 days (most)	Date of service	From primary EOB where applicable

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ERISA self-funded plans can have 60-day windows

Employer-sponsored self-funded plans are governed by the plan's Summary Plan Description (SPD), not state law. Some have filing windows as short as 60 days. Request the SPD for any plan with a short window and set an earlier internal deadline. These plans are your highest CO-29 risk.

What Proof Is Accepted

Accepted vs. rejected proof for timely filing appeals

Accepted by most payers

✅Clearinghouse acceptance report — shows the date the clearinghouse received and accepted the claim for transmission

✅999 / 277CA transaction — payer or clearinghouse acknowledgment confirming receipt within the filing window

✅Prior denial letter from the payer dated within the filing window — proves the payer received it on time even if they denied it

✅Certified mail receipt / delivery confirmation — for paper claims submitted by mail

✅Payer portal submission confirmation — screenshot with timestamp if claim was submitted via payer portal

NOT accepted by any payer

❌PM system charge entry date — this is when you entered the charge, not when it was transmitted

❌PM system batch date — when the batch was created in your system, not when it reached the payer

❌Date of service — irrelevant to filing date

❌Statement that "we always bill on time" — payers require documentation, not attestation

❌Clearinghouse batch export date without payer acknowledgment — shows when you sent it, not when the payer got it

Step-by-Step Response

What to do when you receive CO-29

Pull the clearinghouse submission report immediately
Log into your clearinghouse portal and find the original claim. Look for the acceptance date — when the clearinghouse acknowledged receipt and forwarded to the payer. This is your most important piece of evidence. If the claim was accepted within the payer's filing window, you have a strong appeal. If you cannot find the claim in the clearinghouse at all, the claim may never have been transmitted (a different problem — look for a failed batch or a claim stuck in a hold status in your PM system).
Check for a prior denial or COB sequence that extends the window
Was there a prior denial on this claim for CO-22, CO-16, CO-109, or another reason? Many payers restart the timely filing window from the date of the prior denial, allowing you to resubmit the corrected claim. Was Medicare or another payer involved as primary? Secondary claims often have separate timely filing windows measured from the primary EOB date. Document the full claim history before deciding whether to appeal or write off.
Decide: appeal or write off
If you have proof of timely original submission → appeal. If a prior denial restarts the clock and you are within the window → resubmit corrected claim. If the claim was genuinely filed late with no extenuating circumstances → write off. Do not spend significant appeal resources on a claim you know was filed late — direct those resources to prevention instead.
Submit the timely filing appeal with all proof attached
Send to the payer's appeals address (not the claims address). Include the original claim, clearinghouse acceptance report, cover letter, and any documentation of extenuating circumstances. Check the denial letter for the appeal deadline — most payers require appeals within 30–180 days of the denial. Submit via certified mail or payer portal to create a delivery record. Follow up at 30 days if no response.
Root cause the denial and set up a prevention system
Every CO-29 is a process failure. Identify where the lag occurred: charge entry delay from clinical team, claim stuck in a hold status no one reviewed, COB situation that required an extended submission sequence, or a staffing gap. Set up a filing deadline work queue in your PM system that flags claims approaching their deadline. Report CO-29 volume monthly to practice leadership — it is one of the most avoidable denial types in revenue cycle.

Prevention

How to prevent CO-29 — systems, not effort

Build a filing deadline work queue. Every claim in your PM system should have the payer's timely filing deadline calculated and stored at the time the claim is created. A daily report shows all unsubmitted claims within 30 days of their deadline. This is the single most effective CO-29 prevention tool.
Track charge lag from clinical to billing. The most common root cause of CO-29 is a delay between the date of service and when charges are entered. Set a maximum charge lag standard (typically 3–5 business days) and report exceptions weekly. Late charge entry compresses the time available to submit and correct claims.
Monitor clearinghouse rejection queues daily. A claim can be rejected by the clearinghouse (not reaching the payer) without generating a denial in your system. If rejected claims sit unworked, they accumulate until the filing window closes. Daily clearinghouse queue review prevents this silent failure.
Know the shortest filing window among your payer mix. If you bill any ERISA self-funded plans with 60-day windows, your entire billing process must operate on a 60-day mental model — not on the Medicare 12-month assumption that's safe for most of your volume.
Document secondary claim timely filing separately. Secondary claims (especially Medicare secondary) have different timely filing clocks. Track these claims separately and set a reminder to bill the secondary within 30 days of receiving the primary EOB — long before the secondary's window closes.

Timely Filing Appeal Letter

Appeal template — proof of timely original submission

VIA: Appeals Department — Timely Filing Appeal

Date: [Date] | Payer: [Payer Name] | Claim #: [Claim #]

Member ID: [Member ID] | Patient: [Name] | DOS: [Date of Service]

Provider NPI: [NPI] | Denial Code: CO-29

RE: Timely Filing Appeal — Claim Submitted Within Filing Window

This claim was denied under CO-29 (timely filing limit expired). We are appealing this denial because the claim was submitted within your [X-day] timely filing window.

Original submission date: [Date — from clearinghouse report]
Date of service: [DOS]
Days between DOS and submission: [X days — within window]

Proof of timely submission enclosed:
— Clearinghouse acceptance report dated [date] confirming claim transmission to your system
— [Additional proof: 999/277CA / prior denial letter / certified mail receipt — include whichever applies]

[If COB delay applies, add:] This claim was initially submitted to [primary payer] as required by coordination of benefits rules. The primary EOB was received on [date], and this secondary claim was submitted on [date], within your timely filing window measured from the primary EOB date.

We respectfully request that this denial be overturned and the claim be reprocessed based on the enclosed proof of timely original submission.

Contact: [Name, Phone, Fax] | Practice: [Practice Name]

Frequently Asked Questions: CO-29

CO-29 means the claim was submitted after the payer's timely filing deadline. The only way to overturn it is proof of timely original submission. Without proof, it is a provider write-off that cannot be billed to the patient.

No. CO-29 carries the CO (Contractual Obligation) group code, meaning the balance is a provider write-off. Billing the patient for a CO-29 denial violates your payer contract and may be a compliance issue. The loss belongs to the provider.

Accepted: clearinghouse acceptance report with the submission date and acknowledgment; 999 or 277CA transaction from payer/clearinghouse; prior denial letter from the payer dated within the filing window; certified mail receipt for paper claims. Not accepted: PM system dates (charge entry, batch, export) — those are your internal dates, not evidence that the payer received the claim.

Many payers, including Medicare, allow a new timely filing window from the date of a prior denial when you are resubmitting a corrected claim. This means if you received CO-22, CO-16, or CO-109 first and are now resubmitting after fixing that issue, you may still be within the window. Always verify with the specific payer — the policy varies.

Medicare: 12 months from DOS. TRICARE: 180 days. Most commercial plans: 90–180 days. Medicaid: 90–365 days depending on state. Workers' comp: 1–3 years (state law). ERISA self-funded plans: can be as short as 60 days — check the Summary Plan Description. Always verify in the specific payer contract.

When Medicare is secondary, the 12-month timely filing clock typically runs from the date of the primary payer's EOB, not from the date of service. If you received the primary EOB recently and submitted Medicare secondary shortly after, you are likely still within Medicare's window even if more than 12 months have passed since the DOS.

Prevention requires a filing deadline work queue in your PM system flagging all claims approaching their deadline. Monitor your clearinghouse rejection queue daily for claims that never reached the payer. Track charge lag from clinical to billing and set a maximum lag standard (3–5 business days). Report CO-29 volume monthly by payer and by charge source — most practices can eliminate nearly all CO-29 denials with consistent deadline monitoring.

Related Codes

Timely Filing Limit Expired