- Medicare allows 12 months (365 days) from the date of service to file an initial claim — the most generous major-payer window.
- Commercial payers are far tighter: the Aetna timely filing limit is commonly 120 days, while UnitedHealthcare, Cigna, and Humana commonly allow around 90, all contract-dependent.
- Medicaid timely filing varies by state, often 90–180 days, with some states allowing up to a year.
- A missed window returns CARC CO-29, and the only reliable appeal is documented proof of timely filing — usually a clearinghouse acceptance report.
- Claims rejected at the clearinghouse were never received by the payer, so an unworked rejection queue is the most common cause of unappealable write-offs.
- Your contract overrides every published number: maintain a payer-by-payer deadline matrix and re-verify it annually.
Few denials are as final as a timely filing denial. Most claim problems can be corrected and resubmitted; a claim that arrives after the payer’s deadline is dead on arrival, and the write-off comes straight out of practice profit. The deadlines are wildly inconsistent — a full year for Medicare, an Aetna timely filing limit commonly at 120 days, roughly 90 for UHC and Cigna, and anywhere from 60 days to two years across Blue plans — which is why practices juggling ten payer contracts need a reference table and a prevention workflow, not tribal memory. This guide provides both, plus the appeal path for the rare CO-29 that can be overturned.
What a timely filing limit is — and which clock it runs on
A timely filing limit is the contractual or regulatory deadline for submitting a claim, measured from the date of service (or discharge for inpatient claims). Three clocks matter, and conflating them causes most misses. The initial-claim clock runs from the date of service. The corrected-claim and appeal clocks typically run from the date of the original determination or remittance, not the DOS — so a denied claim usually still has a live path even when the initial window has passed. For secondary claims, many contracts start the clock at the primary payer’s EOB date. Verify each clock in your contract rather than assuming they match.
Aetna timely filing limit and every other payer: 2026 table
The table below reflects commonly published 2026 windows. Every commercial figure is contract-dependent — your participation agreement and the payer’s current provider manual override anything printed here.
| Payer | Typical initial-claim limit | Typical corrected-claim / appeal window |
|---|---|---|
| Medicare (all parts) | 12 months (365 days) from DOS | Redetermination: 120 days from remittance; MA plan appeals commonly ~60 days |
| Medicaid | Varies by state; often 90–180 days, up to 1 year in some states | Varies by state program |
| Aetna | Commonly 120 days from DOS | Appeals commonly ~180 days from determination |
| UnitedHealthcare | Commonly 90 days; some contracts up to 180 | Reconsideration windows commonly cited around 65 days — among the shortest |
| Cigna | Commonly 90 days (per recent policy updates) | Appeals commonly ~180 days |
| BCBS plans | Varies widely by state plan — from ~90 days to 1–2 years | Commonly ~180 days, plan-specific |
| Humana | Commonly 90–180 days depending on contract and plan type | Commonly ~180 days |
Two patterns are worth internalizing. Government programs are generous and commercial plans are not — a practice calibrated to Medicare’s 12 months will routinely blow through 90-day commercial windows. And the same payer name does not mean the same deadline: BCBS is a federation of independent state plans, and national carriers vary limits by product line (commercial vs Medicare Advantage vs Medicaid managed care).
Medicare and Medicaid: the government clocks
Medicare’s 12-month limit, set under the Affordable Care Act, applies uniformly to professional and institutional claims. CMS recognizes only four narrow exceptions: administrative error by Medicare or its contractor, retroactive Medicare entitlement, retroactive entitlement where a Medicaid state agency recouped payment, and retroactive disenrollment from an MA plan. Outside those, a late Medicare claim is not payable and — importantly — the patient cannot be billed for it.
Medicaid runs on state law, and the spread is dramatic: some programs require submission within 90 days, many allow 180, and a few permit up to a year, with separate rules for crossover claims and retroactive eligibility. Treat every state program and managed-care plan as its own row in your deadline matrix.
The CO-29 denial: what it means and why it is nearly final
CARC CO-29 (“the time limit for filing has expired”) is a contractual-obligation denial: the balance is written off, and member cost-sharing generally cannot be transferred to the patient. Unlike a coding or missing-information denial, resubmitting a corrected claim accomplishes nothing — the resubmission is even later than the original. The realistic paths are narrow: prove the claim was actually filed on time, document a qualifying exception (retroactive eligibility, payer system error, incorrect payer information supplied by the member), or absorb the loss. That is why timely filing is fundamentally a prevention problem, not an appeals problem — the same logic that separates it from denials like CO-109 (wrong payer), which are routinely recoverable by redirecting the claim.
Proof of timely filing: the only appeal that reliably works
Payers do sometimes deny claims as late that were submitted on time — misrouted EDI batches, payer ID changes, and adjudication backlogs all happen. There, a proof-of-timely-filing appeal has a genuinely good success rate, but only with acceptance evidence. The two clearinghouse statuses are not equivalent: a claim accepted by the payer (999/277CA acknowledgment) counts as received; a claim rejected at the clearinghouse never reached the payer and proves nothing.
| Evidence | What it shows | Strength |
|---|---|---|
| Clearinghouse acceptance report (277CA) with payer claim number | Payer received and accepted the claim on a specific date | Strongest — the standard for CO-29 appeals |
| EDI batch/999 acknowledgment | File reached the payer’s gateway | Strong supporting evidence |
| Payer portal submission confirmation (screenshot with date and claim ID) | Direct submission on a given date | Strong |
| Certified mail or fax confirmation for paper claims | Delivery date of paper submission | Acceptable |
| Practice-management “claim sent” timestamp alone | Only that your system generated a claim | Weak — usually insufficient |
The appeal packet itself is simple: (1) cover letter stating the original submission date and citing timely submission; (2) the acceptance report highlighting the claim; (3) a copy of the original claim; (4) the remittance showing the CO-29; (5) submission within the payer’s appeal window — which is its own deadline. Our step-by-step appeal guide covers packet structure in detail.
Worked example: how a $4,800 write-off happens (illustrative)
Illustrative scenario. A dermatology practice submits 12 Cigna claims averaging $400 for services performed March 3–5. The clearinghouse rejects all 12 on March 6 for an invalid billing taxonomy — a 30-second fix — but no one works the rejection queue, and the error surfaces in a July aging review, about 120 days after service and past the commonly applied 90-day window. The resubmissions return CO-29. Because the originals were rejected before reaching Cigna, no acceptance report exists and a proof-of-timely-filing appeal has nothing to stand on. Result: 12 × $400 = $4,800 written off — lost to an unworked queue, not a coding error. Multiply by a year of unmonitored rejections and timely filing becomes one of the largest controllable leaks in the revenue cycle.
Prevention workflow: never rely on memory
- Build the deadline matrix. One row per payer/plan/state with initial, corrected, and appeal windows; load the shortest applicable deadline into your PM system’s claim-scrubbing rules.
- Track charge lag daily. Days from service to claim submission should average under 3–5 business days; a rising trend is your earliest warning.
- Work the rejection queue every day. Clearinghouse rejections are the top source of unappealable CO-29s — assign ownership and require same-day rework.
- Run a weekly unbilled/held-claims report. Flag anything unsubmitted at 15 days and escalate at 30.
- Age claims against the payer clock, not a generic 30/60/90. A 75-day-old Cigna claim is near death; a 75-day-old Medicare claim is fine. Days-in-AR targets should reflect that — see our guide to days in A/R.
- Re-verify limits annually. Payers shorten windows in contract updates — Cigna’s widely cited move toward 90 days caught many practices calibrated to 180.
Quick Answers
What is the Medicare timely filing limit? Twelve months (365 days) from the date of service for all claim types, with only narrow exceptions such as retroactive entitlement or contractor error.
What is the Aetna timely filing limit? Commonly 120 days from the date of service for initial claims, though individual contracts and plan types can set different windows — always confirm your participation agreement.
What is the Cigna timely filing limit for 2026? Commonly cited at 90 days for in-network initial claims following recent policy updates, with appeals commonly allowed around 180 days from determination.
Is a CO-29 denial appealable? Rarely — only with documented proof of timely original submission (typically a clearinghouse acceptance report) or a qualifying exception like retroactive eligibility.
Does Medicaid timely filing vary by state? Yes, significantly: windows commonly range from 90 to 180 days, some states allow up to a year, and managed-care plans may impose their own limits.
What to check before you write anything off
- Confirm the actual contract deadline — not the payer’s generic published number.
- Pull the clearinghouse history: was the claim accepted (appealable) or rejected (prevention failure)?
- Check which clock applies — corrected claims and secondaries often run from the remittance or primary EOB date.
- Screen for exceptions: retroactive eligibility, payer-supplied misinformation, system outages.
- Verify the appeal window has not also expired before assembling the packet.
- Log every CO-29 by root cause so the same leak cannot reopen.
Related denial codes and guides
CO-29 sits alongside denials that look similar but behave differently: CO-109 means the claim went to the wrong payer, and refiling with the correct one usually resolves it if done inside that payer’s window. For the broader remittance vocabulary, see our CARC and RARC guide; for structural fixes, a denial management program pays for itself fastest on preventable categories like this one.
Frequently asked questions
Aetna commonly allows 120 days from the date of service for initial commercial claims, with appeals commonly accepted for around 180 days after a determination. Individual contracts and plan types can differ, so the number in your participation agreement always controls.
Only in narrow circumstances. The reliable path is a proof-of-timely-filing appeal backed by a clearinghouse acceptance report or payer acknowledgment showing the claim was received inside the window. Exceptions like retroactive eligibility or payer error can also qualify, but a claim that genuinely missed the deadline is usually a permanent write-off.
The gold standard is a clearinghouse acceptance report (277CA) showing the payer accepted the claim on a specific date, ideally with the payer's claim number. EDI batch acknowledgments, payer portal confirmations, and certified mail receipts also work. A practice-management timestamp alone is usually rejected because it only proves the claim was generated, not received.
Often the corrected-claim or appeal window runs from the date of the original determination or remittance rather than the date of service, giving you a second clock after a denial. But this varies by contract - some payers require corrections within the original filing window, so verify both deadlines before assuming you have time.
Many contracts start the secondary-claim clock at the primary payer's EOB date, since the secondary cannot adjudicate until the primary pays. Slow primary processing can still consume the window, so submit secondaries immediately on receipt of the primary remittance and keep the primary EOB as supporting documentation.