Medicare vs Medicaid Billing: Key Differences for Providers

Program Overview: Medicare vs Medicaid

Both Medicare and Medicaid are government health insurance programs, but they serve different populations and operate under fundamentally different structures. Confusion between them, and between their many sub-programs, is one of the most persistent sources of billing errors in US healthcare.

Medicare is a federally administered program, funded by federal payroll taxes, general revenue, and beneficiary premiums. It was established in 1965 under Title XVIII of the Social Security Act. The Centers for Medicare & Medicaid Services (CMS) sets all coverage rules, billing requirements, and fee schedules nationally. A Medicare claim for a specific CPT code reimburses at the same geographic-adjusted rate whether the patient is in Alabama or Oregon.

Medicaid was established under Title XIX of the same Act. It is jointly funded by the federal government and each state, but each state administers its own program, which means billing rules, covered services, fee schedules, and prior authorization requirements vary from state to state. There are effectively 50 separate Medicaid programs, plus the District of Columbia and US territories. What is covered and reimbursed in Texas may be excluded or paid at a different rate in California.

Who Qualifies for Each Program

Medicare eligibility is primarily age-based and disability-based, without an income test for Parts A and B:

• Adults aged 65 and older (premium-free Part A generally requires about 10 years, or 40 quarters, of Medicare-taxed work by the person or a spouse; others can buy in)
• Adults under 65 who have received Social Security Disability Insurance (SSDI) for 24 months
• Any age with End-Stage Renal Disease (ESRD) or Amyotrophic Lateral Sclerosis (ALS)

Medicaid eligibility is income-based and categorically based, set by each state within federal minimum requirements:

• Low-income adults under 65 (in expansion states, up to 138% of the Federal Poverty Level)
• Children in families meeting income thresholds (also covered under CHIP)
• Pregnant women below state-set income limits
• People receiving Supplemental Security Income (SSI)
• Certain foster care youth and individuals with qualifying disabilities

The key practical difference: Medicare eligibility is relatively predictable from the patient's age and disability status. Medicaid eligibility can change month to month as a patient's income or household situation changes, which is why real-time Medicaid eligibility checks before every visit are required.

Billing Rules and Fee Schedules

Medicare Part B (outpatient physician services) is billed on the CMS-1500 claim form (or 837P electronic equivalent) to your regional Medicare Administrative Contractor (MAC). Reimbursement is based on the Medicare Physician Fee Schedule (MPFS), which CMS updates annually. Rates are adjusted by geographic locality using Geographic Practice Cost Indices (GPCIs). For the current year's conversion factor and RVU values, use the CMS MPFS lookup tool, the same tool used by MACs to calculate payments. See our 2026 Medicare Physician Fee Schedule guide for a breakdown of this year's conversion factor changes and specialty-level impacts.

Medicare generally allows timely filing up to 12 months from the date of service for initial claims. Appeals must typically be filed within 120 days for a redetermination (Level 1), with escalating levels of appeal available through the OMHA (Office of Medicare Hearings and Appeals) and beyond.

Medicaid billing requires enrollment in each state's Medicaid Management Information System (MMIS), a separate portal for each state where you intend to bill. Timely filing limits vary significantly by state: federal rules (42 CFR 447.45) cap the initial filing window at 12 months, and several states are far shorter, such as New York and Massachusetts (90 days) and Texas (95 days). Resubmission windows for corrected claims can run longer. Always verify your state's Medicaid Provider Manual for the applicable limits and covered service list. On average, Medicaid physician fees were 75% of Medicare in 2024 (66% for primary care), with wide variation by state (KFF / Urban Institute fee index).

Medicare Advantage plans (Part C) are administered by private insurers approved by CMS. They must cover at minimum the same benefits as traditional Medicare, but they set their own billing rules, network requirements, and prior authorization policies. Never assume that a Medicare Advantage plan bills or pays like traditional Medicare, operationally, it does not.

Prior Authorization Differences

This is one of the starkest operational differences between the two programs:

Traditional Medicare (Parts A & B) has very limited prior authorization requirements for most physician services. Original Medicare does require prior authorization for some hospital outpatient department services (such as blepharoplasty, botulinum toxin injections, rhinoplasty, vein ablation, cervical fusion, spinal neurostimulators, and facet joint interventions), certain DMEPOS items, and repetitive scheduled non-emergent ambulance transport (CMS prior authorization programs). Since January 2026, the WISeR Model also requires prior authorization (or pre-payment review) for selected services, such as nerve stimulators, skin substitutes, epidural steroid injections, and knee arthroscopy, in six states: Arizona, New Jersey, Ohio, Oklahoma, Texas, and Washington. Advanced imaging (CT, MRI, PET) does not require prior authorization in Original Medicare. But for the vast majority of office visits, E&M services, and standard procedures, traditional Medicare does not require prior authorization.

Medicare Advantage is the exception. MA plans frequently require prior authorization for services that traditional Medicare approves automatically, hospital admissions, specialist referrals, home health, imaging, and many procedures. PA requirements vary by plan and change annually. A patient switching from traditional Medicare to an MA plan mid-year can create a sudden surge in denied claims if your staff is not tracking the change.

Medicaid almost universally requires prior authorization for many services: specialist visits, behavioral health, certain medications, DME, home health, physical therapy, and more. PA requirements are set by each state's Medicaid program and further modified by each Medicaid Managed Care plan. Track PA requirements at the plan level.

Dual-Eligible Patients: Who Pays What

Approximately 12 million Americans are enrolled in both Medicare and Medicaid simultaneously, referred to as "dual-eligible" or "Medicare-Medicaid enrollees" (CMS Medicare-Medicaid Coordination Office). Billing these patients incorrectly is a common and expensive mistake.

The cardinal rule: Medicaid pays last. Bill Medicare (and any other primary coverage, such as an employer plan) first. Most Original Medicare claims for duals cross over to the state Medicaid program automatically through the coordination-of-benefits process, and the Medicare remittance advice shows when a claim was crossed over. Submit a secondary claim to Medicaid yourself only when it doesn't cross over, or when the patient is in Medicare Advantage, attaching the Medicare payment details.

What Medicaid covers as secondary depends on the specific dual-eligible category:

• Full-benefit dual eligibles. Have full Medicaid benefits in addition to Medicare (including QMB-plus and SLMB-plus). Medicaid covers Medicaid-only services and Medicare cost-sharing, subject to state payment limits
• Qualified Medicare Beneficiaries (QMB). Medicaid pays Medicare premiums and cost-sharing. No Medicare provider may bill a QMB for Medicare deductibles, coinsurance, or copays, whether or not the provider accepts Medicaid, and even when Medicaid pays nothing. This applies to Original Medicare and Medicare Advantage (CMS MLN: QMB billing prohibition)
• Partial dual eligibles (SLMB, QI, QDWI). Medicaid pays only Medicare premiums (Part B for SLMB and QI; Part A for QDWI), not cost-sharing. These patients can be billed normal Medicare cost-sharing

Billing a QMB patient for Medicare cost-sharing violates federal law and the Medicare provider agreement, and can lead to sanctions. Patients who complain about such billing can file a complaint with CMS or the State Insurance Commissioner.

Dual-eligible coordination of benefits also applies to pharmacy (Medicare Part D is primary for most drugs over Medicaid) and for long-term care services where Medicaid often covers services Medicare does not.

Enrollment and Credentialing Requirements

You must be separately enrolled in Medicare and in each state's Medicaid program where you intend to bill. Holding a Medicare provider number does not automatically enroll you in any state's Medicaid program, and vice versa.

Medicare enrollment is managed through the Provider Enrollment, Chain, and Ownership System (PECOS). Individual providers enroll using Form CMS-855I; organizations use Form CMS-855B or CMS-855A depending on provider type. The NPI (National Provider Identifier) obtained through NPPES is the same number used for both programs.

Medicaid enrollment is processed through each state's Medicaid portal or paper enrollment process. Requirements, application forms, processing times, and re-enrollment cycles differ by state. Some states require annual re-validation; CMS mandates Medicaid provider re-enrollment every 5 years at minimum. Keep track of expiration dates, billing Medicaid without active enrollment results in claim denial and potential overpayment recovery.

For Medicare Advantage and Medicaid Managed Care plans, you must also complete the plan's own credentialing process, holding government program enrollment alone does not mean you are in-network with MA or MCO plans. See our credentialing guide for the full provider enrollment process.

Side-by-Side Comparison Table