Medicare Advantage (MA) plans and traditional fee-for-service Medicare are frequently treated as interchangeable by billing teams — and that misunderstanding generates a significant volume of avoidable timely filing denials. The rules are fundamentally different, and your workflow needs to reflect that.
Traditional Medicare: 12 Months from DOS
Fee-for-service Medicare (Parts A and B administered through MACs) has a 12-month timely filing requirement from the date of service. This is set by federal statute (42 CFR 424.44) and applies uniformly regardless of provider type, specialty, or claim type. There is no plan-level variation — every traditional Medicare claim must be filed within 12 months.
For inpatient claims, the 12-month window runs from the discharge date, not the admission date.
Medicare Advantage: Also 12 Months, But Watch the Details
CMS requires all Medicare Advantage plans to accept claims for a minimum of 12 months from the date of service (or discharge for inpatient). This is a floor, not a ceiling — some MA plans allow longer windows, but none can go shorter than 12 months under CMS rules.
Here's where billing teams get into trouble: many MA plans are administered by commercial payers (UHC, Aetna, BCBS, Humana) that also have commercial products with much shorter timely filing windows. A UHC commercial claim has a 90-day window. A UHC MA claim has 12 months. If your billing system applies plan-level rules from the payer rather than product-level rules, you will generate false urgency on MA claims and potentially misfile commercial claims.
How to Confirm Plan Type at Point of Billing
The member's insurance card should identify MA plans — look for language like 'Medicare Advantage,' a plan name, or a payer-branded plan with a Medicare beneficiary identifier (MBI). If you're unsure, run eligibility verification and look for the plan type in the 271 response. Don't rely on the payer name alone.
COB: Medicare as Secondary
When Medicare (traditional or MA) is secondary, the timely filing window runs from the primary payer's EOB date, not from DOS. For traditional Medicare secondary, claims are generally due within 12 months of the primary EOB. MA plan COB rules vary — check the specific plan's provider manual, but most follow the same 12-month-from-EOB approach.
Late Filing Exceptions: Narrow but Real
Traditional Medicare allows timely filing exceptions for circumstances beyond the provider's control — retroactive eligibility determinations, administrative errors by Medicare, natural disasters declared under federal emergency provisions, and a few others. These are documented in Medicare Claims Processing Manual Chapter 1. MA plans may or may not offer equivalent exceptions; check the specific plan's provider manual.
Why This Matters for Revenue Recovery
MA claims are often high-value — MA plans cover complex, chronically ill patients who generate significant charges. A billing team that incorrectly applies 90-day commercial rules to MA accounts is writing off recoverable revenue on claims that are well within their actual timely filing window. Audit your denial codes — if you're seeing MA timely filing denials on claims filed at 4–6 months, that's a workflow misconfiguration, not an actual late filing.
Bottom Line
Traditional Medicare and Medicare Advantage both require 12-month timely filing windows under federal rules. The confusion comes from MA plans administered by commercial payers with shorter commercial product windows. Build product-type identification into your billing workflow, not just payer identification, and you'll eliminate this entire category of preventable denials.