Medicaid: What It Is and Why It Matters

Medicaid is the largest source of health coverage in the United States, providing medical assistance to more than 90 million low-income Americans through a joint federal-state financing structure authorized under Title XIX of the Social Security Act. The program covers approximately one in five Americans, finances more than 40 percent of all births nationally, and pays for roughly half of all long-term care services delivered in the country. Understanding Medicaid's eligibility rules, benefit structures, managed care delivery systems, and waiver mechanisms is essential for anyone navigating the health care system -- whether as a beneficiary, provider, caseworker, or policymaker.

This site provides a structured reference library covering the full scope of the Medicaid program. The navigation organizes coverage across eligibility requirements, ACA expansion, state program variation, managed care delivery, covered services, CHIP, dual eligibles, and Section 1115 waivers. Answers to the most common procedural questions appear in the Frequently Asked Questions section.

Federal-state partnership structure

Medicaid operates as an entitlement program jointly funded by the federal government and individual states. The federal government establishes minimum eligibility and benefit requirements through Title XIX of the Social Security Act and associated regulations administered by the Centers for Medicare and Medicaid Services (CMS). States administer their own Medicaid programs within these federal parameters, with significant latitude to expand eligibility, add optional benefits, and structure delivery systems.

Federal funding is provided to states through a matching formula called the Federal Medical Assistance Percentage (FMAP). The FMAP is calculated annually based on each state's per capita income relative to the national average. States with lower per capita incomes receive higher federal matching rates. The statutory FMAP floor is 50 percent (meaning the federal government pays at least half of every Medicaid dollar), and the highest FMAP rates exceed 77 percent for the lowest-income states. For fiscal year 2024, state FMAPs range from 50 percent (for wealthier states like Connecticut and New York) to 77.76 percent (Mississippi).

This matching structure creates powerful fiscal incentives. Every dollar a state spends on Medicaid leverages at least one additional federal dollar, making Medicaid the largest source of federal revenue flowing to most states. However, the matching structure also means that Medicaid costs grow during economic downturns precisely when state revenues decline, creating countercyclical fiscal pressure that Congress has periodically addressed through temporary FMAP increases.

Mandatory and optional eligibility categories

Federal law requires states to cover certain population groups -- known as mandatory eligibility categories -- in order to receive federal Medicaid matching funds. States may also cover additional populations under optional eligibility categories, and most states exercise this flexibility extensively.

Mandatory categories include: low-income families that would have qualified under the Aid to Families with Dependent Children program as it existed in 1996; pregnant women with incomes up to 133 percent of the federal poverty level (FPL); children under age 6 with family incomes up to 133 percent FPL; children ages 6-18 with family incomes up to 100 percent FPL; SSI recipients in most states; and certain categories of Medicare beneficiaries for premium and cost-sharing assistance.

Optional categories that states commonly cover include: pregnant women and infants with incomes above the mandatory thresholds; children and parents with incomes above mandatory levels; the "medically needy" (individuals whose income exceeds Medicaid thresholds but who face medical expenses sufficient to "spend down" to eligibility); institutionalized individuals with incomes up to 300 percent of the SSI benefit rate; and, since the Affordable Care Act, adults ages 19-64 with incomes up to 138 percent FPL under the Medicaid expansion.

The Eligibility Requirements page provides the complete framework for all mandatory and optional categories, income methodologies, and asset test rules.

The ACA Medicaid expansion

The Affordable Care Act of 2010 created a new mandatory Medicaid eligibility category covering all adults under age 65 with household incomes up to 138 percent of the federal poverty level (133 percent FPL plus a 5 percentage point income disregard). This expansion filled the largest gap in Medicaid's historical coverage framework: non-disabled, non-pregnant adults without dependent children, who had been categorically ineligible for Medicaid in most states regardless of income.

The Supreme Court's 2012 decision in National Federation of Independent Business v. Sebelius effectively made the expansion optional for states by ruling that the federal government could not withhold all existing Medicaid funding from states that declined to expand. As of 2024, 40 states plus the District of Columbia have adopted the Medicaid expansion, while 10 states have not. The expansion population receives a higher federal matching rate than traditional Medicaid enrollees -- 90 percent FMAP, compared to the state-specific rates averaging 60-65 percent for other populations.

The expansion's coverage impact has been substantial. An estimated 21 million adults gained coverage through the expansion, and research has documented improvements in access to care, reductions in uncompensated hospital care, decreases in mortality rates, and improvements in state budget stability in adopting states. The ACA Medicaid Expansion page covers the full expansion framework, state adoption timeline, and policy effects.

Managed care and delivery system transformation

More than 70 percent of Medicaid beneficiaries now receive services through managed care organizations (MCOs) rather than traditional fee-for-service arrangements. Under managed care, states contract with private health plans that receive a per-member-per-month capitation payment and assume responsibility for delivering or arranging a defined set of services to enrolled beneficiaries.

Managed care has become the dominant Medicaid delivery model because it offers states predictable per-capita costs, shifts insurance risk to MCOs, and creates organizational structures for care coordination that fee-for-service payment lacks. However, managed care also introduces concerns about network adequacy, service denials, quality measurement, and the appropriateness of directing public health care funds through for-profit intermediaries.

CMS regulates Medicaid managed care through the Medicaid Managed Care Rule (42 CFR Part 438), which establishes requirements for rate-setting actuarial soundness, network adequacy standards, quality measurement, grievance and appeal processes, and enrollment and disenrollment protections. The Managed Care and Delivery Systems page provides the complete regulatory and operational framework.

CHIP: Extending coverage to children

The Children's Health Insurance Program (CHIP), established by the Balanced Budget Act of 1997, provides health coverage to children in families with incomes too high for Medicaid but too low to afford private insurance. CHIP covers approximately 7 million children and is funded through a capped federal allocation with an enhanced matching rate (CHIP FMAP is typically 15 percentage points higher than the state's regular Medicaid FMAP). States can operate CHIP as a Medicaid expansion, a separate child health program, or a combination of both. The CHIP: Children's Health Insurance page details the full program framework.

Dual eligibles and the Medicare-Medicaid intersection

Approximately 12.3 million Americans are "dual eligibles" -- individuals who qualify for both Medicare and Medicaid simultaneously. These individuals are typically aged 65 or older or disabled, with incomes and assets low enough to qualify for Medicaid. Dual eligibles account for a disproportionate share of spending in both programs: roughly 15 percent of Medicaid enrollees but more than 30 percent of Medicaid spending, and roughly 20 percent of Medicare beneficiaries but more than 30 percent of Medicare spending.

The dual-eligible population faces unique challenges navigating two separate insurance systems with different rules, provider networks, formularies, and appeal processes. The Dual Eligibles page covers the coverage coordination framework, Medicare Savings Programs, and integration models.

Section 1115 waivers and state innovation

Section 1115 of the Social Security Act authorizes the Secretary of Health and Human Services to waive certain Medicaid requirements for state demonstration projects likely to promote the objectives of the Medicaid program. These waivers have become the primary mechanism through which states pursue innovative approaches to Medicaid delivery and eligibility -- including work requirements, premium charges, managed long-term services and supports, and substance use disorder treatment reforms.

The waiver process involves a state application, a federal review period with public comment, and a set of terms and conditions that govern the demonstration's implementation, evaluation, and budget neutrality requirements. Waivers are granted for fixed terms (typically five years for new demonstrations, three years for renewals) and must demonstrate budget neutrality -- meaning the federal government should not spend more under the waiver than it would without the waiver. The Waivers and Demonstration Programs page examines the full waiver landscape.

This site -- part of the broader Authority Network America reference infrastructure -- organizes Medicaid's regulatory and operational framework into structured reference pages. For specific procedural questions, the FAQ provides direct answers. For guidance on reaching your state Medicaid agency, enrollment assistance, and advocacy organizations, see the Get Help page.

Read Next

Medicaid Eligibility Requirements The complete framework for mandatory and optional eligibility categories, income counting methodologies, and asset test rules across all states. Medicaid: Frequently Asked Questions Direct answers to the most common questions about Medicaid eligibility, enrollment, covered services, and managed care. ACA Medicaid Expansion How the Affordable Care Act expanded Medicaid to cover adults up to 138 percent FPL, which states adopted expansion, and the coverage impact.