The timely filing limit for Medicare claims is one of the strictest deadlines in medical billing, and one of the most unforgiving. Miss it by even one day and the revenue is gone permanently. No appeal. No second chance. The claim gets denied with a CO-29 code and, in most cases, written off completely.
Understanding medical insurance claim filing time limits across payers is the starting point, but Medicare has its own rules that go deeper than most billing teams realize. Under 42 CFR § 424.44, CMS enforces a strict 12-month filing deadline for all Original Medicare Part A and Part B claims. And Medicare Advantage plans run on completely different, often much shorter, timelines.
This guide covers everything: Part A vs Part B deadlines, every major MA plan’s filing window, the five CMS-approved exceptions, CO-29, corrected claims, and proof of timely filing. The billing team at GenMediTech put this together based on the rules that actually cause denials in practice, no filler, just what protects your revenue.
What Is the Medicare Timely Filing Limit?
The Medicare timely filing limit is 12 months (one calendar year) from the date of service. That deadline applies to all Original Medicare fee-for-service claims, both Part A and Part B, across every Medicare Administrative Contractor (MAC) jurisdiction in the country.
If a service was rendered on March 5, 2025, the claim must be received by the MAC no later than March 5, 2026. One day past that window and Medicare automatically denies the claim, no matter the reason for the delay.
This rule has been in effect since January 1, 2010, under the Affordable Care Act (Section 6404). Before that, providers had up to 27 months depending on participation status. That flexibility no longer exists.
The Most Important Detail Most Billers Miss
Medicare counts the MAC’s receipt date, not the date the claim was submitted, not the date it was created in the billing system, and not the postmark date on a paper claim.
This creates a real risk for paper filers. A claim mailed on the last day of the 12-month window will almost certainly arrive late. For electronic claims, submissions received after 6:00 PM Eastern Time are logged as received the next business day. If that happens on the last valid day, the claim misses the window.
A claim for a service rendered on February 29 (leap year) must be filed by February 28 of the following year since most years don’t have a February 29.
Bottom line: File early. The industry standard practice is to set an internal cutoff at 45 days, not 12 months, so there is always time to correct errors and resubmit before the real deadline closes.
Medicare Part A vs Part B: Two Different Filing Clocks
This is the section that trips up even experienced billers. Part A and Part B do not use the same anchor date to calculate the timely filing window. Getting this wrong leads to avoidable CO-29 denials. Understanding the Medicare timely filing limit claims separately for Part A and Part B is the first step toward eliminating these denials entirely.
Part B: Professional and Physician Claims
For Part B claims (physician visits, outpatient services, diagnostic tests, supplier claims), the timely filing clock starts on the “From” date, the date the service was actually rendered.
Example: A physician sees a patient on January 15, 2025. The Part B claim must be received by the MAC by January 15, 2026.
This applies to:
- Physician office visits
- Outpatient procedures
- Supplier and DME claims
- Laboratory and diagnostic services billed on a CMS-1500
Part A: Institutional and Hospital Claims
For Part A claims (hospital stays, skilled nursing facilities, home health agencies), the clock starts on the “Through” date, the last date in the span of service, not the admission date.
Example: A patient is admitted to a hospital on January 10, 2025 and discharged on January 20, 2025. The Part A claim must be filed by January 20, 2026, based on the discharge date, not admission.
This applies to:
- Inpatient hospital admissions
- Skilled nursing facility stays
- Home health episodes
- Claims billed on a UB-04
Expert Note: For claims billed by physicians and suppliers that include a date span (a “from” and “through” date on the same CMS-1500), the “From” date governs the filing deadline. Only institutional UB-04 claims use the “Through” date.
Original Medicare vs Medicare Advantage: The Filing Rules Are Completely Different
Many providers assume Medicare Advantage follows the same 12-month window as Original Medicare. That assumption causes some of the most common and avoidable timely filing denials in medical billing.
Medicare Advantage plans are run by private insurers that contract with CMS. They set their own filing deadlines, and those deadlines are almost always shorter than 12 months.
Category | Original Medicare (FFS) | Medicare Advantage (MA) |
| Governing authority | CMS / Federal (42 CFR § 424.44) | Private insurer contract with CMS |
| Timely filing limit | 12 months from date of service | 90–180 days (varies by plan) |
| Anchor date | From date (Part B) / Through date (Part A) | Per plan’s provider manual |
| Exceptions available | CMS IOM § 70.7 (5 defined categories) | Per plan’s grievance and appeal process |
| Appeal rights for late claims | Standard appeal NOT available, reopening only | Internal plan appeal (typically 60–120 days) |
| Who enforces it | Medicare Administrative Contractor (MAC) | The individual insurance plan |
The practical risk with MA plans is that there is no single rule to memorize. A practice billing Aetna MA, UHC MA, and Humana MA is managing three different filing windows simultaneously, and none of them are 12 months.
Medicare Advantage Timely Filing Limits by Plan (2026)
Most MA billing teams deal with far more than five plans. Here are the filing limits for the 10 most commonly billed Medicare Advantage plans:
Medicare Advantage Plan | Timely Filing Limit | Key Notes |
| Aetna Medicare Advantage | 120 days from date of service | Resubmissions must meet the same deadline |
| UnitedHealthcare (UHC) MA | 90–180 days | Varies by contract and state, verify provider agreement |
| Humana Medicare Advantage | 180 days | Documentation may allow limited extensions |
| Cigna Medicare Advantage | 120 days | Medicaid-integrated plans may vary |
| Wellcare / Centene | 180 days | Applies to clean claims only |
| Molina Healthcare | 90 days | Strict enforcement, extensions rarely granted |
| Kaiser Permanente | 90 days | In-network providers only |
| Anthem BCBS Medicare Advantage | 90–180 days | State-dependent, check local plan manual |
| Tricare (for Life) | 365 days | Follows Original Medicare rules as secondary payer |
| Blue Shield of CA Medicare Advantage | 120 days | California market only |
2026 Update: These limits reflect current plan policies. Payer contracts update annually, always verified through each plan’s current provider manual before relying on these numbers for billing decisions.
Why Medicare Advantage Windows Are More Dangerous
With Original Medicare, a claim caught 6 months late can still be submitted and paid. With a 90-day MA plan like Molina or Kaiser, that same situation is a permanent write-off.
Practices with high MA volume should maintain separate deadline tracking per payer, not a shared AR queue where all claims age together.
CMS-Approved Exceptions to the 12-Month Filing Limit
The 12-month rule is firm, but CMS recognizes five specific circumstances where a late claim can still be processed. These come from the Medicare Claims Processing Manual (IOM 100-04, Chapter 1, § 70.7). In every case, the provider must document which exception applies and submit a reopening request, not a standard appeal.
Exception Category | What It Means | Documentation Required | Real-World Example |
| Administrative error by CMS or MAC | The delay was caused by a government processing error or system failure | Written proof of the CMS/MAC error, EDI rejection logs, system outage notices, MAC correspondence | CMS EDI system experiences downtime during the final days of the filing window; the claim cannot be accepted electronically |
| Retroactive beneficiary entitlement | The patient’s Medicare eligibility was granted retroactively after the service date | Medicare eligibility letter, SSA documentation showing retroactive coverage dates | Patient was billed under Medicaid at time of service; Medicare entitlement is later granted retroactive to the DOS |
| Retroactive coverage determination | CMS or MAC reverses a prior denial and extends coverage retroactively | MAC reopening notice or CMS correspondence | An old denial is overturned on appeal, creating a new window to file for the original service |
| Administrative appeal or litigation outcome | A court, hearing officer, or CMS appeal authorizes late payment retroactively | Copy of appeal decision or court order | An Administrative Law Judge (ALJ) rules in the provider’s favor after the 12-month window has passed |
| Natural disaster or emergency beyond provider’s control | A declared emergency (hurricane, wildfire, public health emergency) prevents timely submission | FEMA declaration, MAC disaster bulletin, or public health emergency notice | A practice in a hurricane-affected area cannot submit claims during the declared emergency period |
How to Request a Timely Filing Exception
When an exception applies, skip the standard redetermination. Submit a claim reopening request directly to your MAC.
Steps:
- Identify the denied claim (CO-29 or N39011)
- Confirm which CMS exception applies
- Gather supporting documentation
- Submit a Type of Bill ending in “Q” (TOB xxQ) via EDI or paper per your MAC’s instructions
- Attach all evidence with the reopening request
- Monitor MAC correspondence, reopening decisions arrive separately from standard processing
MACs typically process reopening requests within 30–60 days.
Corrected Claims: Do They Follow the Same Timely Filing Rule?
This is one of the most misunderstood areas in Medicare billing. The answer is not a simple yes or no.
Under CMS Change Request 12909 (CR 12909), corrected or adjusted claims submitted after the 12-month window are allowed, but only if the original claim was submitted on time.
So if a provider filed a claim within the window, got paid, then discovered a coding error, the corrected version can still be submitted even after the 12 months have passed.
One important exception within CR 12909: inpatient PPS DRG-increasing adjustments must be submitted within 60 days of the remittance date. Miss that 60-day window and the adjustment is rejected, even if the original claim was filed correctly.
What About RTP (Return to Provider) Claims?
RTP claims, rejected before reaching processing, do not preserve the original submission date. If the corrected version is not resubmitted within the original 12-month window, Medicare treats it as a new late filing.
Rule: Correct and resubmit RTP claims within 10 business days of receiving the rejection. Never let them age.
What Happens When a Medicare Claim Misses the Filing Deadline?
CO-29 and N39011: What These Codes Mean?
When a Part B professional claim arrives after the 12-month window, Medicare issues a CO-29 denial, “The time limit for filing has expired.”
For Part A institutional claims (hospitals, SNFs, home health), the denial appears as N39011 instead.
Both mean the same thing: filed too late, will not be paid. CO-29 also appears on commercial and Medicaid ERAs, the resolution process differs by payer, but for Original Medicare the path is narrow.
What Cannot Happen After a CO-29
- Cannot bill the patient. The financial loss stays with the provider under Medicare’s participation agreement.
- Cannot use the standard appeal process. CO-29 denials are not “initial determinations”, the normal redetermination and ALJ chain does not apply.
The Only Option: Claim Reopening
The only path forward is a claim reopening request, and only if one of the five CMS exceptions applies. If no valid exception exists, the claim is written off.
2026 update, RARC N921 (active March 1, 2026): X12 added this new code meaning “The time limit for filing a reconsideration or appeal has expired.” When both CO-29 and N921 appear on the same remittance, there is nothing left to do. The claim is closed and the appeal window is also gone.
If a dispute ever escalates to Federal District Court (Level 5), the minimum claim amount for 2026 is $1,960, updated annually by CMS.
Practices that regularly see CO-29 denials usually have a process gap, not a one-time mistake. GenMediTech’s AR and Denial Management Services are built specifically to catch these before the filing window closes, not after.
Proof of Timely Filing: What If the CO-29 Is a MAC Error?
Sometimes CO-29 is wrong. A claim submitted on time can be denied as late due to a MAC system error, a silent clearinghouse transmission failure, or a logging issue on the payer’s end.
In these situations, the provider needs documentation proving the claim was submitted within the window.
Strongest proof:
- Clearinghouse 277CA acceptance report, confirms the payer received and accepted the claim. This is not the same as the 999 acknowledgment, which only confirms the clearinghouse received the file.
- EDI submission timestamp with payer acceptance confirmation
Supporting proof:
- Internal billing system log showing claim creation and transmission date
- Clearinghouse portal showing claim status as “accepted” with date
- Payer portal showing claim received before the deadline
What does NOT work on its own:
- A clearinghouse submission report without a 277CA acceptance match
- A postmark or mailing receipt on a paper claim
If a clearinghouse submitted the claim on time but it never reached the MAC due to a clearinghouse failure, that may qualify under the administrative error exception in IOM § 70.7. Get the failure documented in writing from the clearinghouse.
5 Practical Steps to Prevent Timely Filing Denials
Staying compliant with the Medicare timely filing limit requires more than knowing the rule, it requires the right daily process. These are not generic suggestions. These are the specific process gaps that cause most timely filing denials in real practices.
1. Set an internal 45-day cutoff — not 12 months
The 12-month window is the legal limit, not an operational target. Filing within 45 days leaves enough time to catch coding errors, fix clearinghouse rejections, and resubmit before the real deadline closes.
Many billing teams use a timely filing calculator for medical claims to quickly identify the exact last filing date for each claim. It reduces manual tracking errors and helps ensure deadlines are never missed across different payers.
2. Monitor 277CA acceptance reports daily — not just submissions
Submitting a claim is not the same as filing it. A claim that leaves your billing system but gets rejected by the clearinghouse before reaching the MAC is not filed.
- Run 277CA reports daily
- Work any rejected transactions the same day
- Never assume submitted = received
3. Build a separate deadline calendar for each Medicare Advantage plan
One AR aging report will not flag different payer windows. A biller managing Humana MA (180 days), Aetna MA (120 days), and Molina (90 days) needs three separate deadline alerts, not one shared queue.
4. Resolve RTP claims within 10 business days
A Return to Provider (RTP) claim does not preserve the original submission date. If it is corrected and resubmitted outside the 12-month window, Medicare treats it as a brand new late filing. Pull RTP reports daily and close them fast.
5. Verify eligibility the morning of the appointment
A large share of MA-related CO-29 denials happen because the patient switched plans, coverage lapsed, or the biller submitted to the wrong insurer. Catching this before the date of service means the claim never gets filed incorrectly in the first place.
Manual deadline tracking across Medicare, multiple MA plans, and commercial payers is where most practices lose revenue silently. Many small and mid-size practices solve this by working with an outsourced medical billing company like GenMediTech where payer-specific deadline tracking, denial follow-up, and RTP resolution are handled as part of the billing workflow, not as an afterthought.
Conclusion
The Medicare timely filing limit comes down to one strict rule: 12 months from the date of service, with the MAC’s receipt date as the only date that matters.
But the details are where practices lose money:
- Part A and Part B use different anchor dates
- Medicare Advantage plans run on 90–180 day windows, not 12 months
- Corrected claims follow CR 12909, not the standard rule
- CO-29 cannot be appealed, only reopened, and only with a valid CMS exception
- In 2026, N921 is now appearing alongside CO-29, closing even the reopening window
Prevention is the only reliable strategy. A 45-day internal cutoff, daily 277CA monitoring, payer-specific MA tracking, and fast RTP resolution will eliminate the vast majority of timely filing denials before they happen.
One missed deadline is permanent revenue loss. Building the right process around it means it never becomes a problem.
FAQs
What Is the Medicare Timely Filing Limit?
The Medicare timely filing limit for Part A and Part B claims is 12 months (one calendar year) from the date of service, as defined under 42 CFR § 424.44. The Medicare Administrative Contractor (MAC) must receive the claim within this window. The MAC’s receipt date is what counts, not the postmark date or the date the claim was created in the billing system.
What happens if a Medicare claim is filed after the deadline?
The claim is denied with a CO-29 denial code (Part B) or N39011 (Part A institutional claims). The provider cannot bill the patient for the missed amount under the Medicare provider agreement. In most cases, the claim is written off permanently. A claim reopening is the only option, and only if one of CMS’s five approved exceptions applies.
Do Medicare Advantage plans follow the same 12-month filing rule?
No. Medicare Advantage plans are operated by private insurers and set their own timely filing limits. Most MA plans require claims within 90 to 180 days from the date of service, significantly shorter than Original Medicare’s 12-month window. Aetna MA requires 120 days; Molina and Kaiser require 90 days. Providers should verify each plan’s current limit through the plan’s provider manual.
Can a corrected Medicare claim be filed after the 12-month limit?
Yes, if the original claim was submitted on time. Under CMS Change Request 12909 (CR 12909), adjusted or corrected claims are not subject to the standard 12-month timely filing restriction, provided the original claim was filed within the filing window. However, inpatient PPS DRG-increasing adjustments must still be submitted within 60 days of the remittance date.
What counts as proof of timely filing for Medicare?
The strongest proof of timely filing is a clearinghouse 277CA acceptance report, the EDI transaction that confirms the claim was received and accepted by the payer within the filing window. A 999 functional acknowledgment alone does not confirm payer receipt. Internal billing system logs, submission timestamps, and payer portal status showing “received” can serve as supporting documentation.
Can a Medicare timely filing denial be appealed?
Not through the standard redetermination process. Medicare’s timely filing denials (CO-29) are not classified as “initial determinations,” which means the normal five-level Medicare appeal process does not apply. Providers must submit a claim reopening request to their MAC and provide documentation supporting one of the five CMS-defined exceptions. If no valid exception applies, the denial stands.
What is the difference between CO-29 and N39011?
CO-29 is a Claim Adjustment Reason Code (CARC) that appears on Part B professional claim denials when the timely filing limit has been exceeded. N39011 is a Remittance Advice Remark Code (RARC) that appears on Part A institutional claim denials (hospitals, SNFs, home health) for the same reason. Both mean the claim was filed outside the allowed window, they just apply to different claim types.
What is the Medicare timely filing limit for secondary claims?
When Medicare is the secondary payer (after another insurer processes the claim first), the timely filing clock typically starts from the date the primary payer’s Explanation of Benefits (EOB) is issued, not the original date of service. The provider generally has 12 months from the primary payer’s EOB date to submit the claim to Medicare as secondary. Always verify with the specific MAC jurisdiction.
