What is the single most useful attachment?

The clearinghouse acceptance report. It establishes the date the claim was actually transmitted and accepted, which is frequently earlier than the date the payer recorded as received.

Does asking for the payer's record of receipt help?

It often does. It reframes the appeal from an assertion into a reconciliation of two dated records, and it obliges the reviewer to look at the claim history rather than the denial reason alone.

CO-29

Appeal letter template: timely filing limit expired (CO-29)

For denials asserting the claim arrived late. Built around proof of the original submission date, which is what actually overturns these.

Free, no signup required to read or copy it. Replace every bracketed field before sending, and refer to the patient by initials and account reference only — never a full name.

Use this when

The remittance shows CO-29 or states the filing time limit has expired.
You hold a clearinghouse acceptance report showing timely transmission.
Coordination of benefits delayed the secondary claim.
Coverage was applied retroactively after the filing window closed.

The letter

[PRACTICE NAME]
[PRACTICE ADDRESS]
[PHONE] · [FAX]

[DATE]

[PAYER NAME] — Appeals Department
[APPEALS ADDRESS FROM YOUR REMITTANCE]

RE: Appeal of claim denial
Claim number: [CLAIM NUMBER]
Patient reference: [PATIENT INITIALS] / [ACCOUNT REFERENCE]
Date of service: [DATE OF SERVICE]
Billed amount: [AMOUNT]
Denial code: CO-29 — the time limit for filing has expired

To the Appeals Department:

We are appealing the denial of the claim identified above, which was denied as untimely.

[CHOOSE THE PARAGRAPH THAT MATCHES YOUR SITUATION AND DELETE THE OTHERS]

[IF YOU HAVE PROOF OF TIMELY SUBMISSION] This claim was originally submitted on [ORIGINAL SUBMISSION DATE], within the filing period applicable to our agreement. The attached acknowledgment confirms transmission and acceptance on that date. A resubmission of a claim originally filed on time should not be re-dated for timely filing purposes. We ask that the claim be adjudicated using the original submission date.

[IF COORDINATION OF BENEFITS CAUSED THE DELAY] This claim could not be submitted until the primary payer completed adjudication. The primary payer's remittance is dated [PRIMARY REMITTANCE DATE] and is attached. This claim was submitted [SECONDARY SUBMISSION DATE], within the filing period measured from that date.

[IF ELIGIBILITY WAS RETROACTIVE] Coverage for this patient was established retroactively on [RETROACTIVE DETERMINATION DATE], after the date of service. The filing period could not begin before coverage was known to exist. Documentation of the retroactive determination is attached.

[IF THE CLAIM WAS MISROUTED] This claim was originally submitted to [OTHER PAYER] on [DATE] based on the coverage information available at the time of service, and was redirected to your plan upon notification. Documentation of the original submission is attached.

If your determination relies on a received date later than the date evidenced above, we request the payer's record of receipt for this claim so the discrepancy can be reconciled.

Attached in support of this appeal:
[LIST ATTACHMENTS — clearinghouse acceptance report, submission history, primary remittance, eligibility documentation]

We ask that you reprocess this claim and remit payment in the amount of [AMOUNT].

Please provide a written determination within your stated appeal-response window. If any additional documentation would assist the review, contact me directly at [PHONE] or [EMAIL].

Sincerely,

[NAME]
[TITLE]
[PRACTICE NAME]
[NPI / TAX ID]

How to adapt it

The clearinghouse acceptance report is the whole case. Attach it, and reference its date in the letter rather than describing it vaguely.
Requesting the payer's record of receipt is deliberate — it shifts the question from your word against theirs to two documented dates.
If you genuinely filed late and none of the paragraphs apply, this letter will not change the outcome. Spend the time on the next claim instead.

Understand the denial first

CO-29CO-29 denial: timely filing limit expiredThe payer says the claim arrived after its filing deadline — so it will not consider the claim at all.

Common questions

What is the single most useful attachment?: The clearinghouse acceptance report. It establishes the date the claim was actually transmitted and accepted, which is frequently earlier than the date the payer recorded as received.
Does asking for the payer's record of receipt help?: It often does. It reframes the appeal from an assertion into a reconciliation of two dated records, and it obliges the reviewer to look at the claim history rather than the denial reason alone.

Or skip the blanks entirely

Undeny reads the denial document, fills every one of these fields from it, and tracks the appeal deadline. About three minutes instead of thirty.

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