Timely Filing Limits for Behavioral Health Claims: Deadlines, Proof, and CO-29 Appeals
How timely filing actually works across Medicare, Medicaid, and commercial contracts: which clock applies, what counts as proof of filing, how to appeal CO-29 denials with acceptance evidence, and the aging alarms that prevent them.
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Direct answer
Timely filing limit behavioral health: what operators need to know
How timely filing actually works across Medicare, Medicaid, and commercial contracts: which clock applies, what counts as proof of filing, how to appeal CO-29 denials with acceptance evidence, and the aging alarms that prevent them. Medicare FFS: 12 months from date of service, with limited exceptions; Medicaid and commercial limits vary by state and contract — record each payer's window.
A timely filing limit is the deadline for getting a claim to the payer, and missing it produces one of the least appealable denials in billing — CO-29, a contractual write-off — unless you can prove the claim was actually filed on time. The deadlines differ by program: Medicare fee-for-service allows 12 months from the date of service under the Affordable Care Act's filing rule, with narrow exceptions; state Medicaid programs set their own windows; and commercial limits come from your provider agreement, commonly somewhere between 90 days and a year, sometimes shorter.
Two facts make timely filing a workflow problem rather than a calendar problem. First, a rejected claim usually does not count as filed — only an accepted claim stops the clock, so rejections that sit unworked become future CO-29 denials. Second, secondary claims often run on a different clock, measured from the primary payer's remittance rather than the date of service, per contract. The teams that never write off CO-29 are the ones whose queue knows every claim's deadline and whose files hold acceptance proof for every submission.
Key takeaways
The short version
- Medicare FFS: 12 months from date of service, with limited exceptions; Medicaid and commercial limits vary by state and contract — record each payer's window.
- Only accepted claims stop the clock; a rejection at the clearinghouse or payer front end usually does not count as filing.
- Keep acceptance reports as permanent evidence — the 999 and 277CA trail is what wins a CO-29 appeal.
- Secondary and corrected claims run on their own windows; capture them separately from the original clock.
- Alarm on claim age well before the shortest applicable window, not on the average one.
Take the template with you
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Paste into an appeal when acceptance evidence shows the claim was filed within the applicable window.
Re: Claim [CLAIM NUMBER], member [MEMBER ID], date of service [DOS]. This claim was denied with reason code CO-29 (time limit for filing has expired). Our records show the claim was submitted and accepted within the applicable filing period. Enclosed: (1) the applicable timely filing provision [CONTRACT SECTION / PROGRAM RULE] establishing a filing window of [WINDOW]; (2) the electronic acceptance report(s) dated [DATE(S)] showing acceptance of this claim [BATCH/TRACE NUMBERS]; and (3) the claim as submitted. The claim was filed [N] days after the date of service, within the applicable window. We request that the denial be reversed and the claim processed for payment. Please respond within the timeframe required by the provider agreement and applicable law.
1. Build the deadline map
Populate the map from documents, not memory: the provider agreement, the plan's administrative manual, and the state billing manual, each with a citation and a verified date. Where a contract is silent, ask the payer in writing and file the answer. The shortest window in your payer mix sets the pace for the whole billing operation.
| Program | Typical window | Where the rule lives |
|---|---|---|
| Medicare fee-for-service | 12 months from the date of service | Federal statute and CMS guidance, with specified exceptions |
| Medicare Advantage | Set by the plan contract | Provider agreement and plan manual |
| Medicaid | Varies by state and by managed-care plan | State billing manuals and plan contracts |
| Commercial | Commonly 90 days to 12 months from date of service | Your provider agreement — the contract controls |
| Secondary claims | Often measured from the primary payer's remittance date | Contract terms on coordination of benefits |
| Corrected claims and appeals | Separate windows from original filing | Contract and payer policy; log them as distinct deadlines |
2. Treat acceptance proof as a permanent record
- 01
Keep the full transmission trail
Batch reports, clearinghouse acknowledgments, 999 functional acknowledgments, and 277CA claim-status responses together prove what was sent, when, and whether it was accepted.
- 02
Distinguish accepted from received
The evidence that matters is acceptance into adjudication. A file that was transmitted but rejected at an edit usually never started the clock — which is why rejection reports are timely-filing work, not housekeeping.
- 03
Archive searchably by claim
Proof you cannot retrieve per-claim in minutes is proof you do not have. The appeal window for a CO-29 is short; the retrieval time has to be shorter.
- 04
Cover the odd channels
Paper claims, payer-portal entries, and fax submissions need their own dated evidence — confirmation pages, certified-mail receipts, portal screenshots with timestamps.
3. The CO-29 appeal, step by step
- 01
Verify the payer's math first
Check the date of service, the applicable window from your deadline map, and the payer's received date. Payers occasionally apply the wrong window — especially on secondary claims measured from the primary remittance.
- 02
Pull the acceptance evidence
If the claim was originally submitted and accepted within the window — and denied later for another reason, or lost — attach the acceptance trail with dates highlighted.
- 03
Cite the applicable exception where one exists
Medicare recognizes specified exceptions, such as retroactive entitlement and administrative error; Medicaid retroactive eligibility can also reset the effective window. Name the exception and attach its evidence.
- 04
File within the appeal window
The CO-29 appeal has its own deadline. Submit through the payer's stated channel with the deadline logged, and track the response like any other case.
- 05
Write off consciously, not silently
A true miss with no evidence and no exception is a write-off — but record the root cause. CO-29 write-offs are the most preventable dollars in the denial ledger.
4. Prevent the next one with aging alarms
- Give every claim a filing deadline computed from its payer's window at charge entry, and alarm at a fraction of the shortest window — not at the industry-average 90 days
- Work rejection reports daily; every unworked rejection is a claim whose clock is still running with nothing filed
- Hold unbilled services to the same discipline: documentation and coding queues age against the same deadline the claim will inherit
- Track secondary-claim clocks from the primary remittance date, and alarm on primaries that have not paid in time to leave a secondary window
- Report timely-filing write-offs monthly by root cause — late documentation, unworked rejection, COB discovery, enrollment gaps — and fix the largest feeder first
Common questions
Answers before you build.
What is the timely filing limit for Medicare claims?+
Medicare fee-for-service claims must be filed within 12 months — one calendar year — of the date of service, under the Affordable Care Act's filing rule. CMS recognizes limited exceptions, including certain retroactive-entitlement and administrative-error situations. Medicare Advantage plans set their own contractual windows, which can be shorter.
Does a rejected claim count as timely filing?+
Usually not. Most payers count only claims accepted into adjudication; a claim rejected at the clearinghouse or payer front end typically never started the clock. That is why rejection reports need daily work and why acceptance evidence — not just transmission evidence — is what a CO-29 appeal needs.
Can a timely filing denial be appealed?+
Yes, when you have evidence: proof the claim was accepted within the window, proof the payer applied the wrong window (common on secondary claims), or a recognized exception such as retroactive eligibility. A bare request for leniency without evidence rarely succeeds, because CO-29 is a contractual determination.
When does the clock start for secondary claims?+
It depends on the contract. Many agreements measure secondary-claim filing from the primary payer's remittance date rather than the date of service, but not all. Record the rule per payer in your deadline map, and track primaries that pay slowly enough to threaten the secondary window.
Practical closeout
Use this operator checklist.
- Medicare FFS: 12 months from date of service, with limited exceptions; Medicaid and commercial limits vary by state and contract — record each payer's window.
- Only accepted claims stop the clock; a rejection at the clearinghouse or payer front end usually does not count as filing.
- Keep acceptance reports as permanent evidence — the 999 and 277CA trail is what wins a CO-29 appeal.
- Secondary and corrected claims run on their own windows; capture them separately from the original clock.
- Alarm on claim age well before the shortest applicable window, not on the average one.
Continue through the cluster
Verified customer case studies are added only with customer permission and supporting evidence; none is implied by these operational examples.
Sources & methodology
Trace the operational claims.
Marsa Health Editorial reviewed the primary and research sources below on July 28, 2026. We translate them into workflow controls, distinguish proposals from final rules, and flag where plan, program, state, contract, or clinical requirements vary.
- 01Timely Filing Requirements for Medicare Fee-For-Service Claims Centers for Medicare & Medicaid ServicesCMS provider notice implementing the Affordable Care Act's 12-month timely filing limit for Medicare fee-for-service claims, with reference to limited exceptions.Accessed or rechecked July 28, 2026
- 02Claim Adjustment Reason Codes X12The official, maintained list of claim adjustment reason codes used on electronic remittance advice. Code meanings and status change; the live list controls.Accessed or rechecked July 28, 2026
- 03Health Care Payment and Remittance Advice Centers for Medicare & Medicaid ServicesOfficial explanation of ERA, group codes, claim adjustment reason codes, remark codes, and provider-level balance adjustments.Accessed or rechecked July 28, 2026
- 04Medicaid Retroactive Eligibility: Changes under Section 1115 Waivers MACPACCongressional advisory-commission brief on the federal three-month retroactive-eligibility requirement and state waiver variation.Accessed or rechecked July 28, 2026
- 05How to appeal an insurance company decision Centers for Medicare & Medicaid ServicesFederal overview of internal appeals, external review, notices, and general appeal timing. Plan and state rules can differ.Accessed or rechecked July 28, 2026
- 06External Appeals Centers for Medicare & Medicaid ServicesFederal external-review process and consumer protections.Accessed or rechecked July 28, 2026
- 07CMS Interoperability and Prior Authorization Final Rule CMS-0057-F Centers for Medicare & Medicaid ServicesCurrent implementation dates, decision timeframes, denial-reason requirements, metrics, and API provisions for impacted payers.Accessed or rechecked July 28, 2026
Organizational author. Editorial review covers source accuracy, search intent, workflow boundaries, and human-oversight requirements. This material is educational and does not provide clinical, legal, coding, or coverage advice.
No named clinical or legal expert reviewer is attributed to this version. Marsa Health does not invent reviewer credentials.
Read our editorial methodRevision history
What changed and when
July 28, 2026
Initial publication, source review, and operational editing.