A timely filing denial is one of the few insurance denials where the patient is usually not the one at fault in 2026-2027. Every payer sets a deadline for the provider to submit a claim, and when the provider misses it, the explanation of benefits or remittance shows reason code 29, "the time limit for filing has expired." That code almost always comes with the group code CO, contractual obligation, meaning the provider absorbs the loss under its contract or Medicare rules. Many people still receive a bill for the full amount afterward, and paying it is usually a mistake.
Our guide explains how long each payer allows, who owes the bill under Original Medicare, Medicaid, Medicare Advantage and private plans, the cases where you can still owe, and the short letter that resolves most of these bills. If the balance has already gone to a collector, read the hospital bill sent to collections guide and the debt validation letter answer alongside this page.
Coverage Breakdown
Direct answer: the provider missed its own deadline, so you usually owe nothing
No, in most cases. A timely filing denial (code 29, group CO) is the provider's loss under Original Medicare, Medicaid and in-network contracts in 2026-2027. You may still owe a normal deductible or coinsurance, and you can owe the bill if you gave wrong insurance details.
What the timely filing limit is and who sets it (2026-2027)
Original Medicare sets one national deadline: under 42 CFR 424.44, a claim for services on or after January 1, 2010 must be filed no later than one calendar year after the date of service, and CMS counts the date Medicare receives the claim, not the date it was mailed. Medicaid has a federal ceiling of the same length: 42 CFR 447.45 requires each state Medicaid agency to make providers submit claims within 12 months of the date of service, and a state may choose a shorter limit.
Private plans have no single federal deadline. For commercial insurance, the limit is written into the contract between the provider and the insurer, and it often runs from a few months to a year from the date of service. That is why one provider can have different limits for different insurers, and why your explanation of benefits matters: it names the code and the group that decides who pays.
Original Medicare, Medicare Advantage and Medigap: who owes a late-filed claim (2026-2027)
Original Medicare protects you in writing. Section 70.4 of the CMS Medicare Claims Processing Manual, Chapter 1 (revised October 24, 2024), says that when the provider is responsible for not filing a timely claim, the provider may not charge you for the services except for the deductible and coinsurance that would have applied had Medicare paid. The same section says an untimely filing denial is not an initial determination, so the provider cannot appeal it through the formal Medicare appeals channels.
Section 70.6 adds one wrinkle: a provider that believes the patient caused the delay can say so on a no-payment claim, and you keep the usual appeal rights to dispute that. Medigap policies pay only after Original Medicare approves a claim, so a Medigap plan will not pay a denied claim either, and you should not owe the amount in the first place. Medicare Advantage plans follow the provider's contract with the plan, so ask the plan whether the provider is contracted and read the hold-harmless terms.
Medicaid and private plans: hold-harmless rules for a late-filed claim (2026-2027)
Medicaid enrollees are protected by the participation rule. Under 42 CFR 447.15, a provider that takes part in Medicaid accepts the state's payment as payment in full, so a claim the state never pays because of a late filing does not turn into a bill for you. Your own cost-sharing, where your state charges it, is the exception. Because the federal 12-month ceiling is a ceiling, check your state agency's provider manual if a shorter limit is cited on your denial.
Employer and ACA-compliant individual plans work through contracts. An in-network provider agrees to accept the plan's allowed amount and to look to the plan, not to you, for payment, and most contracts say a claim denied for late filing cannot be passed to the member. The wording differs by contract, so ask the insurer's member services line to confirm that the provider is in network and that the denial carries group code CO rather than PR, patient responsibility.
When you can still owe a timely filing bill (2026-2027)
Five situations can leave you responsible, so check them before you send any letter. Compare the list below with your explanation of benefits and your records, because a provider that raises one of these has to document it.
- You gave the provider the wrong insurance, an old card, or no insurance information at registration, so the claim went to the wrong payer. Medicare's manual lets a provider assign the late filing to the patient in that case.
- The denial carries group code PR (patient responsibility) instead of CO, which shifts the amount to you under the payer's remittance rules.
- The provider is out of network and has no contract that holds you harmless. Plan documents and your state's law then decide.
- You, not the provider, were supposed to file, as with some out-of-network claims you submit yourself, and your plan's deadline passed.
- Your normal deductible or coinsurance. Even when the provider cannot bill the insurer's share, Medicare's manual lets it bill the cost sharing you would have owed anyway.
Alternatives: the one-paragraph letter and four other ways to remove a timely filing bill
A short written letter to the provider's billing office resolves most of these bills in 2026-2027, and it works better than a payment plan because a payment plan treats the debt as yours. State the facts in one paragraph: the account number, the date of service, that your explanation of benefits shows reason code 29 with group CO, that under the provider's contract or Medicare rules you may not be billed for this amount, and that you ask for the balance to be adjusted to zero and written confirmation within 30 days. Send it by certified mail and keep a copy. Add the letter to the file even if you also call.
- Call your insurer's member services: ask for the claim history, confirm the provider's network status, and ask the insurer to tell the provider in writing that the member is held harmless. Use the number on your card and note the date and the representative's name.
- Check the group code on the remittance: ask the insurer for the explanation of benefits or remittance advice. Group CO means the provider absorbs the loss; PR means the insurer treats the amount as yours, and you can ask why.
- File an internal appeal if the insurer says the claim was filed on time or the denial code is wrong: HealthCare.gov says you generally have 180 days from receiving the denial notice, and the insurer must decide within 30 days for services you have not received or 60 days for services already received.
- Contact your state insurance department or Medicaid agency if the provider keeps billing you after your letter. They accept complaints about balance billing and can contact the provider or plan.
- Run the bill through the CoveredUSA Bill Analyzer to check the remaining charges for errors before you pay any portion, such as a deductible or coinsurance the provider still claims.
If a timely filing bill has already gone to collections (2026-2027)
A collection notice does not change who owes the amount, but it does start a clock. The Consumer Financial Protection Bureau says that in certain situations you only have 30 days after you are contacted to ask for certain information, so send your dispute in writing promptly and keep proof of mailing. Attach the explanation of benefits showing code 29 and group CO, and ask the collector to verify the debt and to stop collecting until it does.
Send a copy of the same letter to the provider's billing office as well, because the provider decides whether to recall the account. Do not make a partial payment or agree to a payment plan while the dispute is open, since either can be read as accepting the debt. If the provider refuses to recall the account, file complaints with your state insurance department and the CFPB.
Frequently Asked Questions
Is a timely filing denial the patient's fault?
Usually no. A timely filing denial means the claim reached the payer after its deadline, and the provider submits claims, so the provider normally bears the loss. The exception is when you gave wrong or missing insurance information, or when you were the one supposed to file. Check the group code: CO is the provider's responsibility, PR is yours.
What is the timely filing limit for Original Medicare?
Original Medicare requires claims to be filed no later than one calendar year after the date of service, under 42 CFR 424.44, and CMS counts the date Medicare receives the claim. Exceptions are narrow, such as a Medicare contractor error or retroactive Medicare entitlement. The same 12-month rule applies to Part A and Part B claims in 2026-2027.
Can the provider bill me if Medicare denies for timely filing?
Generally no. CMS Claims Processing Manual Chapter 1, section 70.4, says that when the provider is responsible for the late claim, it may not charge you except for the deductible and coinsurance that would have applied had Medicare paid. Medigap will not pay the denied claim, but you should not owe the Medicare portion.
What is the timely filing limit for Medicaid?
Federal rule 42 CFR 447.45 requires each state Medicaid agency to make providers submit claims within 12 months of the date of service, and a state may set a shorter limit. A participating provider accepts Medicaid payment as payment in full under 42 CFR 447.15, so a late-filed Medicaid claim should not become your bill in 2026-2027.
What does CO-29 mean on my explanation of benefits?
CO-29 pairs claim adjustment reason code 29, "the time limit for filing has expired," with group code CO, contractual obligation. The group code assigns the adjusted amount to the provider under its contract. If you see PR-29, the amount was assigned to you as patient responsibility, and you should ask the insurer why.
What should I write to the provider about a timely filing bill?
Write one paragraph with your account number and date of service, state that your explanation of benefits shows reason code 29 with group code CO, say you may not be billed for this amount under the provider's contract or Medicare rules, and ask for a zero balance and written confirmation within 30 days. Send it by certified mail.
Can I appeal a timely filing denial?
You can appeal an insurer's decision, generally within 180 days of the denial notice according to HealthCare.gov, if you believe the claim was filed on time. Under Original Medicare, an untimely filing denial is not an initial determination, so the provider cannot appeal it formally. Your remedy is the letter, not an appeal.
What if the bill was already sent to collections?
Dispute it in writing within 30 days of the collector's contact, because the CFPB says certain rights depend on a 30-day window. Attach the explanation of benefits showing code 29 and group CO, ask the collector to verify the debt, and do not pay or agree to a plan until it does. Copy the provider's billing office.
