Key Takeaways
- Timely filing denials (CO-29) are the cruelest in medical billing: they recover at roughly 11%, the lowest of any major denial category, and Medicare untimely denials cannot even go through the standard appeal process.
- Medicare gives 12 months from the date of service. Most commercial payers give only 90 days. That gap is where practices lose money.
- Your contract can override the published default. Always verify against your signed participation agreement, not a blog post.
- Proof of timely filing means EDI acceptance reports (999/277CA) and clearinghouse submission logs, not “we sent it.”
- Prevention beats appeals: submit within 30 days of service, follow up at 60, escalate at 90.
Why Timely Filing Denials Are the Cruelest Denials in Medical Billing
Most denials are arguments. A coding denial says “you coded it wrong” – you fix the code and resubmit. A medical necessity denial says “prove it was needed” – you send records. There is a path back.
A timely filing denial (Claim Adjustment Reason Code 29) is not an argument. It is a closed door. The payer is not disputing your coding, your documentation, or your medical judgment. It is saying the clock ran out, and the rules give it no discretion to care why.
The numbers are brutal. Industry claims-benchmark reporting puts timely filing denials at roughly 5% of total denial volume, but they recover at an average rate of only about 11% – the lowest recovery rate of any major denial category. Compare that to coding-error denials, which recover around 72%, or missing-information denials at roughly 78%. For every other denial type, the appeal is the strategy. For timely filing, prevention is the only strategy that works.
Medicare makes this explicit: a claim denied as untimely does not qualify as an initial determination, which means it cannot be appealed through the standard Medicare appeals process at all. It can only be reopened under a narrow set of CMS exceptions. Miss the 12-month window and the revenue is gone, with almost no recourse.
This is why every billing operation needs two things: a payer-by-payer deadline reference, and a submission cadence that never lets a claim get near the edge. This guide is both.
Timely Filing Limits by Payer (2026)
The table below reflects standard in-network timelines from payer provider manuals and CMS regulations, verified October 2026. Two warnings before you use it:
- Your contract controls. Participation agreements can and do override published defaults. Build your real reference from signed contracts.
- Deadlines change. Payers revise these limits. Re-verify quarterly against the payer’s current provider manual.
| Payer | Initial claim deadline (from date of service) | Key notes | Verified |
|---|---|---|---|
| Medicare Part A & B | 12 months (1 calendar year) | 42 CFR section 424.44; the MAC’s receipt date controls, not your send date | Oct 2026 |
| Medicare Advantage | 90 to 365 days (plan-specific) | Set by the MA plan, not CMS; many plans use 365 days | Oct 2026 |
| Medicaid | 90 days to 12 months (state-specific) | Each state sets its own limit; federal rules cap state limits at 12 months | Oct 2026 |
| Aetna (commercial, in-network) | 90 days | Out-of-network: 12 months (reduced from 27 months effective Jan 2022) | Oct 2026 |
| Cigna (commercial, in-network) | 90 days | Out-of-network: 180 days; some employer plans allow up to 1 year | Oct 2026 |
| UnitedHealthcare (commercial) | 90 days | Some contracts allow 180 days; Medicare Advantage commonly 365 days | Oct 2026 |
| Humana (commercial) | 90 days | Medicare Advantage: 365 days | Oct 2026 |
| Anthem / BCBS | 90 days (most states) | BCBS is not one company; each state affiliate sets its own limit (some 180 days to 1 year) | Oct 2026 |
| Tricare | 1 year | Federal program; consistent nationwide | Oct 2026 |
The pattern is obvious: commercial payers cluster at 90 days, government programs at 12 months. A practice that builds its workflow around Medicare’s generous window will bleed commercial claims at day 91. Build for the shortest deadline you bill, not the longest.
Note that corrected-claim windows are separate from initial-claim windows and often run from a different start date. For example, Aetna’s commercial corrected-claim window is typically 90 days from the date of the original EOB or remittance advice, not from the date of service. A claim denied at day 85 does not leave five days to correct; it opens a new 90-day window from the remittance date.
What Counts as Proof of Timely Filing
“We submitted it on time” is not proof. When a payer says it never received your claim, or received it late, only specific documents count:
- EDI acceptance reports. The 999 (implementation acknowledgment) and 277CA (claim acknowledgment) files from your clearinghouse prove the claim left your system and was accepted into the payer’s pipeline, with timestamps. This is your primary evidence.
- Clearinghouse submission logs. Availity, Change Healthcare, and other clearinghouses log every submission with date and time stamps. Pull these before you appeal.
- Certified mail receipts. For the rare paper claim, the certified mail receipt with postmark proves mailing date. Regular mail proves nothing.
- Payer portal submission confirmations. If you file through a payer portal, save the confirmation number and screenshot. Portals occasionally lose submissions.
What does NOT count: your practice management system’s “billed date,” an internal note saying the claim was sent, or a phone rep’s verbal assurance. Payers only accept their own receipt records or independent third-party transmission proof.
Archive EDI acceptance reports for at least 24 months. When a timely filing dispute arises a year later, the team that can pull the 277CA wins; the team that cannot writes off the claim.
The Only Appeal Arguments That Sometimes Work
Be honest with yourself: most timely filing appeals fail. But a narrow set of arguments occasionally succeeds, and knowing them is the difference between a 0% and an 11% recovery rate:
- Payer administrative error. The payer gave wrong filing instructions, misrouted the claim internally, or its system rejected a timely submission. Document the error with names, dates, and reference numbers.
- Proof of timely submission with payer loss. Your 277CA shows acceptance before the deadline, but the payer has no record. This is the strongest argument: you met the deadline, their system lost it.
- Retroactive eligibility. The patient gained Medicaid or other coverage retroactively after the deadline passed. Most states allow filing from the eligibility determination date in these cases.
- Natural disaster or CMS waiver. Hurricanes, pandemics, and system outages have triggered filing extensions. Check whether a waiver covered your service dates and region.
- Corrected claim within the correction window. The initial claim was timely; the correction is late. Many payers (Aetna included) run the correction clock from the remittance date, not the service date. Verify before writing off.
File these appeals fast, with documentation attached on the first submission. A bare “please reconsider” letter without proof is a guaranteed second denial.
For the broader denial playbook, see our guide to revenue cycle management, and our AR aging guide for the follow-up cadence that catches at-risk claims before deadlines hit.
Prevention: The 30/60/90-Day Submission Cadence
Since appeals barely work, the real game is never needing one. Run this cadence:
Day 0-30: Submit. Every clean claim goes out within 30 days of the date of service. Not 45, not “when the biller gets to it.” Thirty days. This single discipline eliminates the majority of timely filing exposure, because even a 90-day payer leaves 60 days of buffer for rejections and corrections.
Day 30-60: Confirm and correct. Verify every claim was accepted (check 277CA reports, not just “sent” status). Fix rejections the same week. A rejected claim that sits for three weeks is a timely filing denial in slow motion.
Day 60-90: Escalate. Any commercial claim unpaid at day 60 gets a status check. Anything unresolved at day 75 gets a phone call. At day 90, commercial claims are at the edge; treat them as urgent regardless of dollar amount.
Ongoing: Watch the calendar, not just the report. AR aging reports show how old a claim is. Your deadline tracker should show how many days remain before each payer’s filing limit. A 100-day-old Medicare claim is routine. A 100-day-old Aetna claim is an emergency. Age alone does not tell you which.
Build the deadline table above into your practice management system or a shared reference sheet, review it quarterly, and tie it to automated alerts at 30, 60, and 75 days. The practices that never lose claims to timely filing are not lucky. They are systematic.
Our medical billing services run this exact cadence: claims out within days of service, acceptance verified weekly, and deadline-tracked follow-up that treats day 75 like the emergency it is.
Frequently Asked Questions
What is the timely filing limit for Medicare?
12 months (one calendar year) from the date of service, under 42 CFR section 424.44. The controlling date is when the Medicare Administrative Contractor receives the claim, not when you send it. If the deadline falls on a weekend or federal holiday, the next business day counts.
What happens if I miss the timely filing deadline?
The claim is denied with Claim Adjustment Reason Code 29 (timely filing), and recovery is unlikely: roughly 11% on average, the lowest of any denial category. For Medicare, an untimely denial cannot go through the standard appeals process at all.
What is the timely filing limit for Aetna?
90 days from the date of service for in-network commercial claims. Out-of-network commercial claims have 12 months. Corrected claims typically get 90 days from the original EOB or remittance date. Always confirm against your participation agreement.
What is the timely filing limit for UnitedHealthcare?
90 days from the date of service for in-network commercial claims, though some contracts allow 180 days. UnitedHealthcare Medicare Advantage plans commonly use 365 days.
Can a timely filing denial be appealed?
Sometimes, but rarely successfully. The arguments that occasionally work: payer administrative error, proof of timely submission that the payer lost (277CA records), retroactive patient eligibility, disaster-related CMS waivers, or a corrected claim filed within the separate correction window. Always attach documentation with the first appeal.
How do I prove a claim was filed on time?
With EDI acceptance reports (the 999 and 277CA files) and clearinghouse submission logs showing timestamps. Your billing software’s internal “billed date” does not count as proof. Archive acceptance reports for at least 24 months.
Losing revenue to missed deadlines? Our free billing audit reviews your submission timelines, denial patterns, and payer-specific exposure, and shows exactly where timely filing risk is hiding. Request your free audit.
Review cadence: payer deadlines change. This table was verified October 2026 and is scheduled for quarterly review.
