The Original Vision for Medicaid Expansion

When Congress drafted the ACA, it envisioned a two-track system for expanding coverage. The marketplace exchanges would serve people above the poverty line who lacked employer-sponsored insurance, while a sweeping expansion of Medicaid would cover those below or near the poverty line — specifically, adults up to 138% of the federal poverty level (FPL). Together, the two tracks were meant to close most coverage gaps.

The law originally required all states to expand Medicaid or risk losing their existing federal Medicaid funding entirely. That coercive mechanism was struck down by the Supreme Court in NFIB v. Sebelius (2012), making expansion effectively optional for states.

The Federal Financing Deal

To incentivize expansion, the federal government offered extraordinarily favorable financing terms. The federal government would pay 100% of costs for newly eligible enrollees from 2014–2016, gradually phasing down to a permanent floor of 90% by 2020 — with states responsible for just 10 cents of every dollar spent on the expansion population.

By comparison, federal matching rates for traditional Medicaid enrollees average around 57%, with some states paying significantly more. The expansion deal was, on purely financial terms, highly favorable to states.

Which States Expanded — and Which Didn't

As of 2024, 40 states plus Washington, D.C. have adopted Medicaid expansion, with several holdout states adopting it years after the initial rollout following ballot initiatives or political shifts. The following states have not expanded as of this writing:

  • Alabama
  • Florida
  • Georgia (has adopted a limited waiver-based alternative)
  • Kansas
  • Mississippi
  • South Carolina
  • Tennessee
  • Texas
  • Wisconsin (covers adults up to 100% FPL but hasn't adopted full ACA expansion)
  • Wyoming

The holdout states are concentrated in the South, and they tend to share both conservative political leadership and higher rates of uninsured residents among low-income adults.

The "Coverage Gap" Problem

In non-expansion states, adults whose income falls below the poverty line face a particularly cruel irony: they earn too little to qualify for ACA marketplace subsidies (which begin at 100% FPL) but too much to qualify for traditional Medicaid in their state. This gap leaves several million adults in non-expansion states without any affordable coverage option — a direct consequence of the Supreme Court decision making expansion optional.

Arguments Against Expansion

Governors and legislators in non-expansion states have offered several objections:

  • Long-term fiscal risk: Even at a 10% state match, the cost of a large expansion population represents a significant ongoing budget obligation, particularly if federal matching rates are reduced in the future.
  • Medicaid's existing quality problems: Critics argue that adding more enrollees to a program with low provider reimbursement rates and access limitations doesn't meaningfully improve health outcomes.
  • Work requirements: Several states have sought federal waivers to impose work or community engagement requirements on expansion adults — an approach that courts have repeatedly blocked but that remains politically appealing in conservative-leaning states.

What the Research Shows

A substantial body of research has examined the effects of Medicaid expansion in states that adopted it early. Commonly documented outcomes include reductions in uncompensated care costs at hospitals, increased rates of cancer screening and diagnosis, and improvements in some measures of financial security for low-income households. Research on mortality effects is more contested, with some studies finding reductions in preventable deaths and others finding more modest impacts.

The Unfinished Map

More than a decade after the ACA passed, the Medicaid expansion map remains incomplete. The holdout states collectively contain a disproportionate share of the nation's uninsured population. Whether those states ultimately expand — through legislation, ballot initiative, or some modified waiver arrangement — remains one of the most consequential unresolved questions in American health policy.