Medicare timely filing limit 2026: the 12-month rule, exceptions and payer comparison

The Medicare timely filing rule in 2026

The limit comes from Section 6404 of the Affordable Care Act, which cut the old filing period to 12 months for services furnished on or after January 1, 2010. CMS put it into regulation at 42 CFR 424.44 and explains it in Chapter 1, Section 70 of the Medicare Claims Processing Manual. Nothing changed for 2026: a Part A or Part B fee-for-service claim must be filed with the Medicare Administrative Contractor no later than 12 months, or one calendar year, after the date the service was furnished.

Two words in that sentence do most of the damage. The first is "filed." A filed claim is a submission the contractor has received and that has passed its edits for completeness and validity. A claim the clearinghouse rejected, or the MAC returned as unprocessable, was never filed. The second is "received." The receipt date the contractor stamps on the claim is what counts, so a claim transmitted on the last day and received the next morning is late.

How the date of service is counted

For professional claims on the CMS-1500 or 837P, the clock starts on the line item From date. If a line spans several dates and the From date is outside the window while the To date is inside, the contractor splits the line and denies the untimely portion. For institutional claims on the UB-04 or 837I with a From and Through span, such as an inpatient stay, the Through date starts the clock, which gives hospitals slightly more time on a long admission. CMS even addresses leap years: a service on February 29 must be filed by February 28 of the following year.

What the deadline does not cover

The limit applies to the initial claim. Once a claim is filed on time, a later correction to the same services falls under the reopening and administrative finality rules in Chapter 34 of the manual rather than the filing limit. What you cannot do is add a service or line left off the original claim after the 12 months have passed; that addition is treated as a new claim.

The four exceptions CMS allows

42 CFR 424.44(b) lists four situations in which the contractor may extend the limit. Each extends the window to the last day of the sixth calendar month after the triggering event, not indefinitely.

1. Administrative error. The failure to file on time was caused by an error, delay or misrepresentation by a Medicare employee, contractor or agent acting within its authority. The extension runs six months from the month the error was corrected and the provider or beneficiary notified. No extension is granted for a service more than four years old.
2. Retroactive Medicare entitlement. The patient was not entitled to Medicare on the date of service and later received notice of entitlement retroactive to or before that date. The extension runs six months from the notification.
3. Retroactive entitlement involving a state Medicaid agency. The patient was covered by Medicaid only, later became entitled to Medicare retroactively, and the state recouped its payment from you six months or more after the service. The extension runs six months from the recoupment.
4. Retroactive disenrollment from a Medicare Advantage or PACE plan. The patient was enrolled in an MA or PACE plan on the date of service, was later disenrolled retroactively, and the plan recouped its payment six months or more after the service. The extension runs six months from the recoupment, and you must document the prior enrollment, the disenrollment notice and the recoupment.

Notice what is not on the list. Staff turnover, a software conversion, a clearinghouse outage on your side or a lost superbill are not exceptions. For those, CMS instructs the contractor to assume the provider accepts responsibility.

What happens when a claim is filed late

A late claim comes back on the 835 remittance with claim adjustment reason code CO-29, "the time limit for filing has expired," often paired with a remark code telling you the decision cannot be appealed. Section 70.4 of the manual is explicit: a denial for untimely filing is not an initial determination, so it is not subject to the five-level appeal process that begins with a redetermination request within 120 days.

There is one narrow door. If the claim was received on time and the receipt date is wrong, you can ask the contractor for an informal review and supply proof. Proof means the 277CA acknowledgment showing the MAC accepted the claim on a date inside the window, not a screenshot of your practice management system showing when a batch was created. Keep every 277CA for at least 18 months for this reason.

The financial rule is the part that hurts. Where the provider is responsible for the late filing, the beneficiary cannot be charged for the service except the deductible and coinsurance that would have applied had Medicare paid. The rest is a write-off, and it should be tracked by reason code so it shows on the monthly denial report. Our guide on how to reduce claim denials covers that loop.

Medicare Advantage and Medicaid follow different rules

Medicare Advantage plans are run by private insurers under contract with CMS, and the 12-month fee-for-service rule does not govern their filing limits. Each plan sets its window in the provider participation agreement. Windows of 90 to 180 days from the date of service are common for contracted providers, though some plans allow longer, and the limit for non-contracted providers can differ from the contracted one. Unlike Original Medicare, MA plans operate their own payment dispute and reconsideration process, so a late-filing denial from an MA plan can sometimes be disputed with proof of timely submission under the plan's rules. Read the agreement rather than assuming.

Medicaid sits under a federal ceiling with state discretion below it. 42 CFR 447.45(d) requires state Medicaid agencies to require providers to submit all claims no later than 12 months from the date of service, with limited carve-outs, including claims that were first submitted to Medicare, which may be paid within six months after the Medicare disposition. States may set shorter windows and many do, and Medicaid managed care organizations set their own contractual limits, so a dual-eligible patient can involve three different clocks on the same date of service. Our state billing pages note the program structure for each state we serve.

Timely filing limits by payer type: a comparison

The table below is a planning reference, not a substitute for the contract. Where a figure varies by contract or state, that is what the table says.

The Medicare number is the longest limit most practices face, so a workflow built around "we have a year" will miss every other payer. Let the shortest limit in your payer mix set the internal deadline: if your largest commercial contract says 90 days, bill every encounter inside 30.

Building a filing calendar that holds

The claims that miss the Medicare window are rarely the routine ones. They fell out of the normal flow: a claim held for a coding query nobody answered, an encounter never charged because the provider did not close the note, a rejection that sat in a clearinghouse queue nobody owned. A filing calendar is the set of reports that surfaces those cases before the deadline does.

The three reports that catch late claims

• Unbilled encounters by date of service. Run weekly from the scheduling and EHR systems, not the billing system, which only knows about charges already entered. Anything older than 30 days needs a named owner.
• Rejected and returned claims by original date of service. Sort by age, not by rejection date. A claim rejected three times has been aging since the first date of service the whole time.
• Held and pended claims. Coding queries, missing authorizations and eligibility holds pause the claim; none of them pause the clock. Any Medicare claim within 60 days of its limit is escalated regardless of the hold reason.

Secondary and crossover claims

When Medicare is secondary, the 12-month clock still runs from the date of service, not from the primary payer's remittance, so a slow primary adjudication eats into it. When a claim crosses from Medicare to Medicaid, the state's post-Medicare window applies. Track both dates on the account, and if the primary has not adjudicated within 90 days, escalate rather than wait.

How this fits with denial work

A CO-29 is almost never recoverable, so the useful question is not how to appeal it but which process produced it. Group the last year of CO-29 write-offs by payer, hold reason and the step where the claim stalled; one or two causes usually account for nearly all of them.

DyBilling runs claim submission and denial management inside the client's existing practice management system with a payer-specific filing calendar and a 60-day escalation rule for any claim approaching its limit. A free billing audit will show how many of last year's write-offs carried CO-29 and where those claims stalled.