Timely Filing Limits: When Your Provider's Late Claim Becomes Your Bill (2026)

1. What a timely filing limit actually is

Every payer — Medicare, Medicaid, and every commercial insurer — sets a hard deadline by which a provider must submit a claim. Every payer sets a deadline for receiving claims, and missing that deadline can lead to denied reimbursement. That deadline is called the timely filing limit, and it runs from the date of service, not the date you got the bill or the date your insurer sent an explanation of benefits.

The deadline is entirely the provider's responsibility. You did not agree to it, you are not a party to the provider's contract with the insurer, and you have no control over when a billing department submits a claim. The timely filing limit exists so payers can close their books and process claims while documentation is still fresh — it is an administrative rule between the provider and the payer, full stop.

When a provider misses the deadline, the insurer issues a denial. Insurance will deny the claim with denial code CO-29 — "the time limit for filing has expired" — whenever the claim is submitted after the time frame. That denial code is critical for patients to recognize, because it tells you the rejection was caused by the provider's own late filing, not by anything wrong with the service, the coding, or your coverage.

2. The federal deadlines that govern this — and where to find them

The rules are clearest for government programs, which is where most billing disputes end up. For Medicare, the requirement is set in federal regulation, not just internal policy. Under 42 CFR § 424.44, claims for services furnished on or after January 1, 2010 must reach the Medicare Administrative Contractor (MAC) no later than one calendar year from the date of service. A service performed on July 1, 2025 must reach the MAC by July 1, 2026, or it will be denied as untimely regardless of mailing delays.

For Medicaid, the federal ceiling is set in a different regulation. Under 42 CFR § 447.45(d)(1), the state Medicaid agency must require providers to submit all claims no later than 12 months from the date of service. That is a ceiling, not a floor: states can set shorter windows, and many do. Check your state Medicaid agency's provider manual for the exact deadline that applied to your claim.

For Medicare Advantage — the privately administered version of Medicare — the rules differ slightly. No single federal regulation sets a filing deadline for Medicare Advantage claims. For contracted providers, the window comes from the provider's contract with the plan, and it is often shorter than Original Medicare's 12 months. 42 CFR § 422.520 is sometimes cited for this, but it governs how fast the plan must pay or deny a claim (for example, 95 percent of clean claims from non-contracted providers within 30 days), not how long a provider has to file one. If you're enrolled in a Medicare Advantage plan, check the plan's evidence of coverage or provider manual for the exact window.

Commercial insurers set their own deadlines through provider contracts. Most commercial payers give 90 to 365 days; some give as few as 60. Those timelines are set in the provider's participation agreement, not in your insurance policy — which is why patients often have no idea the deadline even exists until a bill arrives.

3. Why a CO-29 denial cannot legally become your bill (in most cases)

Here is the core protection you need to know: if a claim is not filed within the timely filing limit, it will be denied — and the provider cannot bill the patient. If you look at the terms of any insurance company contract, you'll almost certainly see a clause indicating that the payer isn't responsible for any claims received outside its timely filing limit. If the deadline is missed, the provider can neither bill the patient for the visit nor appeal to the payer. Instead, they have to write it off.

For Medicare patients, this prohibition is ironclad. For Medicare and Medicaid patients, providers generally cannot bill the patient for a timely filing miss because late filing is treated as provider error, which means the practice absorbs the entire loss with no ability to recover it. For commercial payer patients, the answer depends on the specific contract and state law, but in most cases the contract prohibits billing the patient as well, leaving the write-off as the only outcome regardless of payer type.

A timely filing write-off happens when a claim is not submitted within the insurance company's required timeframe. Every payer has strict deadlines, and missing them can result in claim denial. When this happens, the provider may have no choice but to write off the entire amount, especially if the delay was their responsibility.

There is one scenario where you could owe something even after a CO-29: if you had already paid a copay at the time of service and the EOB comes back showing zero patient responsibility. A practice would write off the late-filed portion and, if the EOB does not state a patient responsibility, keeping a patient payment already collected is considered fraud. If you paid a copay upfront and later see that the claim was denied for timely filing with zero patient responsibility assigned, ask the provider's billing office to return that payment.

4. Comparison table: timely filing limits by payer type in 2026

Use this reference table to understand the deadlines that should have applied to your claim before it was denied.

For context on out-of-network billing more broadly, see our guide to what upcoding is and how hospitals inflate your bill — a different but related billing error that also shows up on itemized statements.

5. How to spot a timely filing error on your bill and what to do

You won't always be told why a claim was denied before you receive a bill. Here's how to detect a timely filing problem yourself.

Step 1: Get your Explanation of Benefits (EOB). Your insurer must send you an EOB every time it processes — or denies — a claim. The EOB will show the denial reason. If you see "CO-29," "time limit expired," or "untimely filing," that is the provider's problem, not yours. If you are unfamiliar with EOB terminology, our post on what "adjustments" on a hospital bill really mean in 2026 walks through how to read each line.

Step 2: Match the date of service to the applicable deadline. Using the table above, identify what window applied to your specific payer. Then check the date the claim was actually submitted (your EOB or a call to your insurer can confirm this). If the submission date falls outside the window, CO-29 is the expected result — and the balance is on the provider.

Step 3: Contact the provider's billing department in writing. State that the denial was issued for CO-29 (timely filing), identify the applicable regulation or contract clause, and request written confirmation that the balance will be written off and not sent to collections. Keep a copy of everything.

Step 4: If the provider refuses, escalate. File a complaint with your state insurance commissioner's office. For Medicare claims, contact your Medicare Administrative Contractor. The provider's refusal to write off a CO-29 denial is a contract violation, and in the Medicare context it can constitute a federal billing violation. Read our guide on when a hospital can send you to collections under 2026 federal rules — a CO-29 balance that was never yours to owe should not appear on a credit report.

6. Narrow exceptions: when a provider might legitimately re-bill after a late filing

Not every situation is black and white. There are a small number of recognized exceptions where a timely filing deadline can be extended — but they work in favor of the provider getting paid by the insurer, not in favor of billing you. You should know them to avoid being misled.

Medicare regulations at 42 CFR § 424.44(b) allow for the following exceptions to the one calendar year time limit for filing fee-for-service claims: administrative error, if failure to meet the filing deadline was caused by error or misrepresentation of an employee, Medicare contractor, or agent of the Department that was performing Medicare functions and acting within the scope of its authority. Another exception involves retroactive Medicare entitlement, where a beneficiary receives notification of Medicare entitlement retroactive to or before the date the service was furnished.

The timely filing limit cannot be extended beyond December 31 of the third calendar year after the year in which the services were furnished. For services furnished during October through December of a year, the time limit may be extended no later than the end of the fourth year after that year. These exceptions exist to let providers recover payment from Medicare under unusual circumstances — they do not create any new category of patient liability.

The No Surprises Act adds a separate layer of protection for specific scenarios. The 2020 No Surprises Act established new federal protections against surprise medical bills and balance billing, most of which took effect January 1, 2022. It bans balance billing for out-of-network emergency care and for post-stabilization care until the patient can consent and safely be moved to an in-network facility. If your CO-29 denial involves an out-of-network provider at an in-network facility, the No Surprises Act may give you an additional shield even if the general timely filing rules did not. Our full breakdown of what the federal IDR process means for your medical bill in 2026 explains how payment disputes between providers and insurers get resolved in those scenarios.

7. Decision tree: should you dispute this bill, request documentation, or pay?

Use this visual to quickly assess what to do when a bill arrives that you suspect stems from a timely filing denial.

For a broader look at the kinds of errors that appear on hospital bills — including phantom charges and duplicate line items — see our reference on how to read every line of your itemized hospital bill in 2026.

About VerifyDoc: We help patients identify errors and overcharges on medical bills. We publish guides on hospital billing, the No Surprises Act, and disputing medical charges, updated as federal and state rules change.