What is Medicare (Part A & Part B Traditional / CMS)'s timely filing limit for initial claims?

Medicare (Part A & Part B Traditional / CMS) enforces an initial claim timely filing deadline of 1 calendar year (365 days) from Date of Service.

How many days do you have to appeal a denial with Medicare (Part A & Part B Traditional / CMS)?

Appeals and payment disputes with Medicare (Part A & Part B Traditional / CMS) must be filed within 120 calendar days from date of Medicare Summary Notice (MSN/RA).

What is the secondary claim timely filing limit for Medicare (Part A & Part B Traditional / CMS)?

Secondary claims for Medicare (Part A & Part B Traditional / CMS) must be submitted within 1 calendar year from Date of Service.

Medicare Federal Government / CMS 365 Days Limit

Medicare (Part A & Part B Traditional / CMS) Timely Filing Limit & Appeal Deadlines

Official filing rules, submission windows, appeal timeframes, and acceptable electronic clearinghouse proof for billing Medicare (Part A & Part B Traditional / CMS).

Initial Claim Limit

365 Days from DOS

Secondary Claim Limit

365 Days from EOB

Level 1 Appeal Limit

120 Days

Level 2 Dispute Limit

180 Days

1. Initial Claim Submission Deadline

1 calendar year (365 days) from Date of Service

Clean electronic 837P or 837I claims must be received and acknowledged by Medicare (Part A & Part B Traditional / CMS) within this window. If a claim is rejected on front-end clearinghouse validation (Level 2), it is not considered received by Medicare (Part A & Part B Traditional / CMS) until corrected and successfully re-transmitted.

2. Specific Filing Rules for Medicare

Governed by federal statute: Section 6404 of the Affordable Care Act requires claims to be filed within 1 calendar year of DOS.

Exceptions to 365-day deadline: Administrative error by CMS/MAC, retroactive Medicare entitlement, retroactive Medicare and Medicaid dual eligibility.

Redetermination (Level 1 Appeal) must be filed within 120 days of RA date.

Reconsideration by Qualified Independent Contractor (QIC / Level 2) must be filed within 180 days of Redetermination.

3. Accepted Proof of Timely Filing

Official Proof Required by Medicare

Certified clearinghouse 277CA acceptance acknowledgment, Fiscal Intermediary Standard System (FISS) direct data entry timestamp, or Medicare Administrative Contractor (MAC) portal tracking.

Important: Screenshots from your internal billing software or electronic health record (EHR) showing the date a claim was created are not accepted by Medicare as proof of submission. You must supply clearinghouse 277CA acceptance reports.

4. Appeal Letter Template for Medicare

Use this standardized appeal letter to overturn a CO-29 timely filing denial when you have verifiable clearinghouse proof:

RE: Timely Filing Denial Appeal (CO-29)
Payer: Medicare (Part A & Part B Traditional / CMS)
Patient Name: [Patient Name] | Member ID: [Member ID]
Date of Service: [Date of Service] | Claim ID: [Claim Number]
Billed Charges: $[Billed Amount]

Dear Appeals Coordinator,

We are submitting this formal appeal in response to the timely filing denial (CO-29) issued on the Explanation of Benefits dated [Remittance Date]. Under our participating agreement with Medicare (Part A & Part B Traditional / CMS), the timely filing limit is 365 calendar days from the date of service.

The original claim was electronically transmitted and received prior to the timely filing limit expiration. Enclosed please find Exhibit A: The clearinghouse Electronic Data Interchange (EDI) 277CA Claims Acknowledgment Report confirming successful gateway acceptance on [Date of Initial EDI Transmission] with Payer Claim Control Number [ICN / CCN].

Because this documentation constitutes conclusive objective proof of timely electronic submission, we respectfully request that the claim be reprocessed and approved for reimbursement.

Sincerely,
[Billing Manager / Practice Representative]
[Practice Name]
[Phone Number]