Medicare Timely Filing Limit: The 12-Month Rule, the Four Exceptions, and What to Do After a CO-29

Medicare gives you 12 months from the date of service. File one day past that window and the claim denies, you can't appeal it, and you can't bill the patient for the balance.

The Medicare timely filing limit sits at 12 months, or one calendar year, under 42 CFR 424.44. The part that trips up experienced billers is which date counts. Medicare measures the day your Medicare Administrative Contractor receives the claim, not the day you submitted it.

Miss the window and CO-29 shows up on your remittance. That denial never becomes an initial determination, so the appeal process doesn't open at all. A reopening request is the only path left, and it works only when one of four CMS exceptions applies to your claim.

Below, you'll find how the clock gets measured and why Part A and Part B start counting on different dates. The four exceptions come next, along with what to do on Monday morning when a CO-29 lands.

Medicare timely filing limit at a glance

Filing limit: 12 months (one calendar year) from the date of service

Governing rule: 42 CFR 424.44

Anchor date, Part B: the "From" date on the CMS-1500

Anchor date, Part A: the "Through" date on the UB-04

What counts as filed: receipt by the correct MAC, not submission and not the postmark

Denial code: CO-29 on Part B, N390 on Part A institutional claims

Appeal rights: none. A late-filing denial is not an initial determination

Only remedy: a reopening request, and only when a documented CMS exception applies

What Is the Medicare Timely Filing Limit?

Medicare requires claims to reach the appropriate contractor no later than 12 months after the date the service was furnished. That rule applies to Part A and Part B fee-for-service claims across every MAC jurisdiction, and it hasn't changed for 2026. You can read the regulation itself at 42 CFR 424.44 on eCFR.

The 12-month window took effect for services furnished on or after January 1, 2010, under Section 6404 of the Affordable Care Act. Before that, providers had somewhere between 15 and 27 months depending on the date of service and participation status, as CMS Transmittal R2140CP describes.

That older window is gone. Medicaid.gov confirms the same effective date, and no MAC extends the deadline past one year on its own authority.

Is the Medicare filing limit one year or two years?

One year. The two-calendar-year figure comes from pre-2010 guidance, and it still turns up in older training decks and on certification practice exams. If a staff member quotes two years to you, they learned it from material that predates the Affordable Care Act change.

The Medicare timely filing limit governs Original Medicare only. Medicare Advantage plans run on a separate set of rules, covered further down.

How Medicare Measures the 12-Month Clock

The Medicare timely filing limit runs against one date only: the day the correct MAC receives your claim. Your submission date, your billing system timestamp, and the postmark on a paper envelope carry no weight in that calculation.

A submission becomes a filed claim on the day the correct Medicare contractor receives it. From that point on, the claim carries a permanent receipt date in its record, per CMS receipt date guidance.

The wrong contractor resets nothing

Send a claim to the wrong MAC and it isn't a claim yet. Medicare treats it as filed only once the correct contractor receives it.

Practices that opened a location in a new state, or that changed jurisdictions after a merger, lose claims this way and rarely trace the cause. Our guide to how MACs process claims walks through the jurisdiction structure.

When the deadline lands on a weekend

If the last day of the filing period falls on a Saturday, Sunday, legal holiday, or another federal nonworkday, the deadline moves to the next succeeding workday. That's written into the regulation, and it buys you a day or two on claims that would otherwise expire over a holiday weekend.

Paper filers get no such cushion on transit time. A claim mailed on day 364 won't arrive on day 365.

What counts as "filed" for Medicare timely filing

Filing date: the date the correct MAC receives the submission

Not the filing date: your submission date, your billing system date, or the postmark

Wrong contractor: a claim sent to the incorrect MAC isn't filed until the correct MAC receives it

Deadline on a nonworkday: moves to the next succeeding workday

Permanent record: once accepted, the claim carries a permanent receipt date

Does Medicare use the submission date or the receipt date?

Medicare uses the receipt date. A service furnished on March 5, 2025 needs to reach the MAC by March 5, 2026, regardless of when your team clicked submit.

Part A vs Part B: Two Different Filing Clocks

Part A and Part B don't start counting on the same date. Getting this backward on a long inpatient stay or a rental item produces CO-29 denials that look inexplicable until someone checks which date the system used.

Part B professional claims run from the line-item date or the claim statement "From" date. That covers office visits, outpatient procedures, diagnostics, and supplier claims billed on a CMS-1500 or an 837P.

Part A institutional claims with span dates run from the "Through" date. A patient admitted on January 10, 2025 and discharged on January 20 gives you until January 20, 2026, not January 10.

The split that catches DME and therapy claims

On a professional claim carrying a date span, one line can be untimely while another is still inside the window. Contractors split the line item and deny the untimely portion, which is how a single claim comes back partly paid and partly denied. The CMS Claims Processing Manual, Chapter 1 sets out the measurement rules.

Services from two different calendar years can't ride on one claim either. Anyone billing across December 31 needs to split the claim, and the place of service coding rules apply separately to each.

Medicare Timely Filing Deadlines by Claim Type (2026)

Submitted Is Not the Same as Filed

A claim that left your billing system hasn't necessarily been filed. That gap between sent and received is where most preventable timely filing losses start, and it shows up in three different forms.

A rejected claim never entered the Medicare processing system. Missing or invalid data stopped it at the door, so it doesn't appear on a remittance advice and carries no appeal rights. Correct the data and resubmit inside the original window.

Claims returned to provider, or RTP, don't count as filed for timely filing purposes. If nobody corrects them before the temporary storage period ends, the record can be purged with no permanent trace, because Medicare never treated them as claims.

A denial is different. Medicare made a payment determination, it appears on your remittance advice, and most denial reasons carry appeal rights. Timely filing is the exception to that, covered next.

Through all three, the clock keeps running. A rejection sitting in a work queue for 40 days burned 40 days of your filing window.

Rejection vs RTP vs denial under Medicare

Rejection: never entered the processing system. Not on the remittance advice. No appeal rights. Correct and resubmit within the original window

RTP (Returned to Provider): not considered filed for timely filing. Can be purged with no permanent record if nobody corrects it in time

Denial: a payment determination. Appears on the remittance advice. Most denials carry appeal rights

The clock: keeps running through all three. A rejection doesn't pause the filing period

Does a rejected claim reset the timely filing clock?

No. A rejected claim doesn't pause or restart the 12-month period. The clock started on the date of service and it runs continuously, whatever happens to the claim in between.

What Happens When a Medicare Claim Misses the Deadline

Claims that miss the Medicare timely filing limit come back with CO-29, and that's a harder stop than most billers expect. CO-29 is the claim adjustment reason code for an expired filing limit on Part B professional claims.

Part A institutional claims carry remark code N390 instead, which some MACs display as N39011. DME claims commonly show reason code 29 paired with remark code N211. Three codes, three claim types, one meaning.

You can't appeal a CO-29

A determination that a claim wasn't filed timely isn't an initial determination, which means it isn't subject to appeal. The regulation sits at 42 CFR 405.926(n), and CMS Transmittal R830CP carries the same language.

HHS clarified the point in 2006 and it hasn't moved since. You can read the HHS guidance on untimely claims directly.

Untimely claims get stopped in processing before coverage edits and audits ever run. No initial determination exists, so the five-level appeal ladder never opens. Filing a redetermination request on a CO-29 is wasted labor.

You can't bill the patient either

Where the provider is responsible for the late filing, you may not charge the patient beyond the deductible and coinsurance that would have applied if Medicare had paid. The write-off stays with the practice.

A reopening request is the only remedy, and it works only when a documented CMS exception applies. If none does, the claim is unrecoverable. Our denial management services team sorts recoverable CO-29 claims from write-offs before anyone spends hours on the wrong ones.

The operational cost lands somewhere unexpected. A biller spends three weeks assembling an appeal packet nobody will read, while claims still inside their filing window sit untouched in the queue. Our breakdown of common denial reasons covers the same pattern across other codes.

Where a Medicare CO-29 denial leaves you

Denial code: CO-29 (Part B), N390 (Part A institutional), reason code 29 with N211 (DME)

Appeal rights: none. A late-filing denial isn't an initial determination (42 CFR 405.926(n))

Redetermination: not available. The five-level appeal process doesn't open

Patient billing: prohibited beyond the deductible and coinsurance that would have applied if Medicare had paid

Only remedy: a reopening request, and only with a documented CMS exception

No exception: the claim is a write-off

Looking at a CO-29 on your remittance right now? The first question is whether a CMS exception applies, and that's a documentation review rather than an appeal. Send us the denial and the dates, and we'll tell you straight when a claim isn't recoverable.

The Four CMS Exceptions to the 12-Month Limit

Four exceptions to the Medicare timely filing limit sit at 42 CFR 424.44(b). Several billing guides publish five, usually adding natural disasters or litigation outcomes while dropping one of the four that CMS recognizes. Medicaid.gov lists them the same way CMS does.

1. Administrative error

A Medicare employee, contractor, or agent of the Department made an error or gave you wrong information while acting within the scope of its authority. That error is what caused you to miss the deadline.

2. Retroactive Medicare entitlement

The beneficiary wasn't entitled to Medicare when you furnished the service. After your filing period expired, they received notice of entitlement effective retroactively to or before that date of service.

3. Retroactive entitlement involving a State Medicaid agency

Medicaid covered the patient on the date of service. Medicare entitlement came through later, backdated, and the state Medicaid agency took its payment back six months or more after the service date.

4. Retroactive disenrollment from an MA plan or PACE organization

The patient was enrolled in a Medicare Advantage plan or a Program of All-inclusive Care for the Elderly when you furnished the service. A later disenrollment took effect retroactive to or before that date, and the plan recouped its payment six months or more afterward.

How long the extension runs

Granted exceptions extend the filing period through the last day of the sixth calendar month following the triggering month. The trigger differs by exception, which is the part that changes your deadline math. CMS Transmittal 12909 carries the current manual language.

Medicare Timely Filing Exceptions and Extension Triggers (42 CFR 424.44(b))

Two ceilings nobody mentions

Administrative error requests get refused once you pass four years from the date of service. Contractors won't accept them beyond that point no matter how well documented the error was.

A second ceiling applies across the board. The filing limit can't stretch past December 31 of the third calendar year after the year the services were furnished. For services furnished October through December, that extension can run no later than the end of the fourth year.

Is a natural disaster a Medicare timely filing exception?

No. The four regulatory exceptions don't include a general natural-disaster category. During declared emergencies, CMS and individual MACs sometimes issue separate waiver instructions, which is a different mechanism from the standing exceptions at 42 CFR 424.44(b).

How to Request a Timely Filing Exception

Send a reopening request, not an appeal. Appeals departments can't grant timely filing waivers, so a redetermination request lands in the wrong queue and comes back unanswered.

1. Identify the denied claim and confirm the denial code (CO-29, N390, or reason code 29 with N211).
2. Confirm which of the four exceptions applies. If none applies, stop. The claim isn't recoverable.
3. Gather the documentation that supports that specific exception.
4. Submit the reopening request through your MAC's stated process. Part A institutional providers generally use a type of bill ending in Q. On the CMS-1500, note administrative error situations in Item 19.
5. Monitor the request separately, because a reopening decision doesn't arrive through normal claim processing.

That last step is where practices lose track. A reopening sits outside your usual claim status workflow, so it needs its own follow-up cadence. Our AR follow-up services team runs reopenings on a separate tracker for exactly that reason.

Documentation by exception

• Administrative error: written evidence of the error, EDI rejection logs, system outage notices, contractor correspondence
• Retroactive entitlement: the Social Security Administration or Medicare entitlement letter showing the retroactive effective date
• Medicaid recoupment: the state Medicaid agency letter reflecting the recoupment
• MA or PACE disenrollment: dated Common Working File eligibility screen prints, or proof of the plan's recoupment

Contractors weigh each request on its own evidence, as CMS retroactive entitlement guidance describes. Nobody can promise an outcome on a reopening, and any billing company that does is guessing.

Exception requests fail more often on documentation than on eligibility. If claims are sitting past the window and you're not sure which ones have a real exception behind them, that's worth a second set of eyes before your team spends the hours.

Corrected Claims and Reopenings Under Medicare

Whether you can correct a claim past the deadline depends on what you're changing. Adding something is governed by one rule. Fixing something already on the claim is governed by another. Most guides collapse the two and get the answer wrong.

Adding an item or service

An adjustment that adds an item or service left off the original claim isn't permitted once the filing limit expires. Institutional providers use a type of bill ending in 7 to add charges, and only while the claim sits inside the filing period.

Correcting information already submitted

No separate timely filing period governs adjustments as such. When an adjustment corrects or supplements information that was already on a timely-filed claim, administrative finality and reopening rules apply instead of the one-year filing rule, per CMS Transmittal 12909.

Both statements floating around the industry turn out to be true at once. "Corrected claims must be within 12 months" describes adding. "Adjustments have no filing period" describes correcting. Adding isn't correcting, and the distinction decides whether your claim gets paid.

Past the window, use a reopening

Institutional corrections made after the filing limit go through the reopening process with a type of bill ending in Q. Submit the same correction as a type of bill ending in 7 and it comes back to you unprocessed. The CMS reopening manual sets out the timeframes.

One carve-out sits inside the adjustment rules. An adjustment that produces a higher-weighted DRG on an inpatient PPS claim needs to reach Medicare within 60 days of the remittance for the original claim.

Rejected and unprocessable claims aren't corrections at all. Fix the data and resubmit as a new claim, inside the original 12-month window.

Correcting a Medicare claim: which route applies

Adding an item or service left off the original claim: not permitted after the filing limit expires

Correcting information already on a timely-filed claim: handled under administrative finality and reopening rules, not the one-year filing rule

Institutional adjustment to add charges: type of bill ending in 7, only inside the filing period

Correction after the filing limit: reopening request, type of bill ending in Q

Higher-weighted DRG adjustment: within 60 days of the remittance for the original claim

Rejected or unprocessable claim: correct and resubmit as a new claim, inside the original 12-month window

Do corrected claims have to be filed within 12 months?

It depends on what you're changing. Adding an item or service left off the original claim isn't permitted past the filing limit. Correcting information already submitted on a timely claim falls under reopening and administrative finality rules instead.

Does Medicare accept corrected claims with frequency code 7?

Medicare handles corrections through its adjustment and reopening processes rather than the replacement-claim conventions many commercial payers use. Institutional adjustments and reopenings get identified by type of bill, and the correct code depends on whether the claim is still inside its filing window.

Medicare Advantage Timely Filing Is a Different Rule

Medicare Advantage plans don't run on the 12-month rule, and they don't uniformly run on 90 days either. CMS sets a minimum filing window that MA organizations have to allow, under 42 CFR 422.520.

Non-contracted providers get that full minimum window, because MA plans pay them under Original Medicare rules. Contracted providers get whatever the participation agreement specifies, and agreements often set 90 or 180 days.

Why MA claims are more dangerous than Original Medicare

A claim caught six months late under Original Medicare is still submittable. That same claim under a contracted 90-day agreement is a permanent write-off, and no exception process brings it back.

Two rules follow. Never apply a commercial 90-day window to an MA claim without checking the agreement first. Never write off an MA claim as untimely until you know whether you're contracted with that plan. Enrollment status decides which rule governs, and our Medicare enrollment guide covers in detail.

Plans including UnitedHealthcare, Aetna, Humana, Cigna, and the Blue Cross Blue Shield affiliates each set their own contracted windows. Published day counts move between contract years, so your signed agreement is the only reliable source.

Corrected claims and appeals under MA

The manual provisions covering corrected claims apply to Original Medicare fee-for-service. Medicare Advantage corrected-claim timing follows the participation agreement instead.

Appeals split as well. MA plan reconsiderations go to the plan and typically run around 65 days from the denial notice, a different clock from Original Medicare's 120-day redetermination window.

Original Medicare vs Medicare Advantage Timely Filing Rules (2026)

Timely Filing Limit vs Appeal Filing Limit: Two Separate Clocks

The Medicare timely filing limit governs how long you have to submit the original claim. A separate clock, the appeal filing limit, governs how long you have to challenge a denial once it lands. Miss the second and you forfeit the claim even when you hit the first.

One caveat before the table. These appeal deadlines cover coverage and payment denials. A CO-29 timely filing denial goes through reopening and never enters this ladder at all.

Medicare Appeal Filing Deadlines by Level (Original Medicare)

The five-day presumption that shortens your window

Medicare presumes you received the initial determination five calendar days after the date printed on the notice, unless you can show otherwise. Counting 120 days from the notice date instead of the presumed receipt date gives you roughly 115 usable days. The CMS appeals manual sets out the full process.

Levels 3 and 5 carry amount-in-controversy thresholds that CMS adjusts each year, so check the current figures before you plan an escalation. Our guide to unpaid claim recovery covers how to prioritize which denials are worth appealing at all.

Two clocks, different rules, and both run whether anyone's watching or not. If your team tracks filing deadlines but nobody owns appeal deadlines, that's usually where the recoverable money goes quiet. Worth auditing before the next aging report.

Timely Filing When Medicare Is the Secondary Payer

Billing the primary insurer first buys you nothing on Medicare's clock. The 12-month period started on the date of service and kept running while you waited for the primary payer's determination.

A primary payer that takes eight months to adjudicate has consumed two-thirds of your Medicare window. Teams that only open the Medicare claim after the primary EOB arrives are working with the remainder, not a fresh year.

Track MSP claims against the original date of service rather than the primary payer's response date. When a primary payer slow-walks a determination, escalate it, because the delay costs your Medicare window and not theirs.

Secondary claim timing varies between payers, and Medicare Advantage plans handle coordination of benefits under their own agreements. Check the plan before you assume a deadline.

What Counts as Proof of Timely Filing

Sometimes a CO-29 is wrong. A claim submitted on time can come back denied as late because of a transmission failure, a routing error, or a logging problem on the payer's side. Documentation is what gets it reversed, and not all documentation carries equal weight.

The 999 and the 277CA aren't the same thing

A 999 functional acknowledgment confirms your clearinghouse received the file. A 277CA confirms the payer received and accepted the claim. Only the second one proves filing, and billing teams that treat a 999 as proof find that out during a dispute. Our 277CA claim tracking guide covers the full acknowledgment sequence.

Proof of timely filing, ranked by weight

Strongest: the 277CA claim acknowledgment showing payer acceptance, with date

Strong: EDI submission timestamp matched to a payer acceptance record

Supporting: internal billing system transmission logs

Supporting: clearinghouse portal showing status accepted, with date

Supporting: payer portal record showing receipt before the deadline

Not sufficient alone: a 999 functional acknowledgment, which confirms the clearinghouse received the file rather than the payer

Not sufficient alone: a postmark or mailing receipt, because Medicare measures receipt rather than dispatch

When the clearinghouse dropped it

If your clearinghouse transmitted on time but the claim never reached the MAC, get the failure documented in writing from the clearinghouse. That letter is what supports an administrative error argument under the exception rules above. Our clearinghouse comparison guide covers reliability and reporting differences between vendors.

How to Calculate Your Medicare Filing Deadline

Four steps, and the first one causes most of the errors.

1. Find your anchor date. Part B uses the line-item or claim "From" date. Part A span claims use the "Through" date.
2. Add 12 months. A service on March 5, 2025 is due March 5, 2026.
3. Check whether that date lands on a weekend or a federal holiday. If it does, the deadline moves to the next succeeding workday.
4. Set your internal target well ahead of it, measured in weeks after the date of service rather than months.

Leap years create an edge case worth building into your tracker. A service furnished on February 29 comes due on February 28 of the following year, since most years have no February 29.

Daily submission cutoffs matter on the final day too. Submissions arriving after a payer's cutoff typically get logged as received the next business day, which turns a timely claim untimely if you're filing on day 365. Cutoff times vary by payer and by clearinghouse, so confirm yours.

How to Stop Losing Claims to Filing Deadlines

Five practices separate the teams that lose claims to deadlines from the teams that don't. None of them require new software.

1. Set an internal cutoff instead of working to the legal one. The Medicare timely filing limit is an outer boundary, and hitting it leaves no room to fix a rejection.
2. Work acceptance reports daily, not submission reports. Reviewing what went out tells you nothing about what came back accepted.
3. Clear RTP claims within days. A returned claim doesn't preserve your original submission date, so an aged RTP becomes a brand new late filing.
4. Track deadlines per payer and per contract. One shared aging report can't flag three different filing windows at once.
5. Verify eligibility before the encounter. A large share of deadline losses begin as a claim sent to the wrong payer, discovered months later.

Practice four is where mixed payer panels break down. A group carrying Original Medicare alongside two contracted MA plans needs three separate deadline alerts, and a single aging queue won't produce them. Our deadline-prioritized AR recovery work sorts claims by filing window proximity rather than dollar value alone.

Manual tracking fails at scale for a reason that has nothing to do with discipline. One person can't hold three payer windows, an RTP queue, and an aging report in their head while the phones are ringing.

That's a capacity problem, and outsourced billing at 2.99% solves it by handing those clocks to someone whose whole job is watching them.

Most practices don't lose claims because someone was careless. They lose them because nobody had the bandwidth to watch three deadline clocks at once. A quick look at your aging report usually shows where the gaps sit.

Working With a Billing Partner on Medicare Deadlines

Four questions separate a billing partner who protects your filing windows from one who reports on them after the fact. Ask each candidate directly.

• Do they track filing deadlines per payer and per contract, or in one shared queue?
• Do they work 277CA acceptance reports daily, or only submission reports?
• How fast do they clear RTP claims?
• Will they tell you when a claim isn't recoverable, instead of billing you for the appeal?

What this costs

Most medical billing companies charge 4% to 7% of collections. MedSole RCM charges 2.99%, and provider credentialing runs $99 per payer enrollment, covering application submission, follow-up, and status tracking through approval. No setup fees, no long-term contracts.

At 2.99% you get eligibility verification, coding review, claim submission, payment posting, denial management, AR follow-up, and reporting. Every service runs inside your existing EHR.

Credentialing delay is a timely filing problem

An unenrolled provider can't bill that payer, but the filing clock on those services runs anyway. Eight weeks of enrollment delay means eight weeks of the window gone before you can submit anything. Combining medical billing and credentialing under one team closes that gap.

The $99 per payer rate covers CAQH profile work, application submission, weekly payer follow-up, and recredentialing deadline tracking. MedSole RCM serves providers in all 50 states across more than 75 specialties.

If you're comparing billing companies, the question worth asking every one of them is what happens to a claim at day 300. Ours get flagged before that. A billing analysis takes about 20 minutes and costs nothing.

Medicare Timely Filing Limit: Frequently Asked Questions

What is the Medicare timely filing limit in 2026?

The Medicare timely filing limit is 12 months, or one calendar year, from the date of service. That rule comes from 42 CFR 424.44, and it applies to Part A and Part B fee-for-service claims in every MAC jurisdiction.

Your claim has to reach the correct contractor inside that window, and Medicare counts its receipt date rather than your submission date. The rule took effect for services furnished on or after January 1, 2010, and Medicaid.gov confirms the current period.

Does Medicare use the submission date or the receipt date?

Medicare uses the date the correct MAC receives your claim. Your billing system timestamp, your clearinghouse submission date, and the postmark on a paper envelope carry no weight in that calculation.

Claims sent to the wrong contractor don't count as filed until the right one receives them. If the deadline falls on a Saturday, Sunday, legal holiday, or federal nonworkday, it moves to the next succeeding workday.

What happens if a Medicare claim is filed after 12 months?

The claim denies with CO-29 on Part B, or N390 on Part A institutional claims. Untimely claims get stopped in processing before coverage edits run, so no initial determination exists.

You can't appeal it, and you can't bill the beneficiary beyond the deductible and coinsurance that would have applied if Medicare had paid. A reopening request is the only remaining option, and it works only when a documented CMS exception applies. Without one, the claim is a write-off.

Can a Medicare timely filing denial be appealed?

No. A determination that a claim wasn't filed timely isn't an initial determination, so it isn't subject to appeal under 42 CFR 405.926(n).

The five-level Medicare appeal process never opens on a CO-29. MAC appeals departments can't grant timely filing waivers, and providers who submit redetermination requests on untimely claims get them back without a decision on the merits. Send a reopening request to your MAC instead, with documentation supporting one of the four CMS exceptions.

What are the exceptions to the Medicare 12-month filing limit?

Four exceptions exist at 42 CFR 424.44(b). Two of them cover errors and coverage. Administrative error by a Medicare employee, contractor, or agent counts, and so does retroactive Medicare entitlement.

The other two involve a payer taking money back six months or more after the service. One is a state Medicaid agency recouping payment. The other is an MA plan or PACE organization recouping after a retroactive disenrollment.

Each granted exception extends filing through the last day of the sixth calendar month following the triggering month. Natural disasters aren't among the four.

Do corrected claims have to be filed within 12 months?

It depends on what you're changing. An adjustment that adds an item or service left off the original claim isn't permitted once the filing limit expires.

An adjustment that corrects or supplements information already submitted on a timely-filed claim falls under administrative finality and reopening rules instead. Institutional corrections made past the window go through a reopening with a type of bill ending in Q. Rejected claims aren't corrections at all, and need resubmission as new claims inside the original window.

Do Medicare Advantage plans follow the same 12-month rule?

No. CMS sets a minimum filing window that Medicare Advantage organizations must allow under 42 CFR 422.520, and non-contracted providers receive that full window because MA plans pay them under Original Medicare rules.

Contracted providers follow whatever their participation agreement specifies, which often runs 90 or 180 days. Applying a commercial 90-day assumption to an MA claim is a common source of avoidable CO-29 denials. Check the signed agreement before writing off an MA claim as untimely.

Can I bill the patient if a claim is denied for timely filing?

No. Where the provider is responsible for the late filing, you may not charge the beneficiary except for the deductible and coinsurance amounts that would have applied if Medicare had paid the claim.

The financial loss stays with the practice. Some practices bill the patient without knowing this restriction exists, which creates a compliance exposure on top of the lost revenue. Write the claim off and fix the workflow that produced the late filing.

What counts as proof of timely filing for Medicare?

The strongest evidence is a 277CA claim acknowledgment showing the payer accepted the claim, with the date. A 999 functional acknowledgment doesn't carry the same weight, because it confirms your clearinghouse received the file rather than the payer receiving the claim.

Supporting documentation includes EDI submission timestamps matched to payer acceptance, internal transmission logs, and payer portal records showing receipt. Postmarks and mailing receipts don't stand alone, since Medicare measures receipt rather than dispatch.

What is the Medicare appeal filing limit?

A redetermination request goes to your MAC within 120 days of receiving the initial determination, and Medicare presumes receipt five calendar days after the notice date.

Reconsideration follows at 180 days, then 60 days each for the ALJ hearing, the Appeals Council, and federal court. These deadlines apply to coverage and payment denials. A CO-29 timely filing denial never enters this ladder, because it isn't an initial determination.

Still not sure whether a specific claim is recoverable? That's usually a five-minute answer once someone looks at the denial code and the dates. Send it over and we'll tell you either way.