A decade after the Affordable Care Act (ACA) expanded Medicaid eligibility and streamlined enrollment, a new study finds that while coverage among eligible individuals has increased nationwide, stark disparities in take-up persist, especially among young adults, rural residents, American Indian and Alaska Native populations, and those living in non-expansion states. The findings come as millions face renewed eligibility checks following the 2023 end of the pandemic-era continuous enrollment policy and as recent federal legislation imposes new administrative hurdles to enroll and maintain coverage.

The study, published May 26 in The Milbank Quarterly, analyzes population-wide data from more than 2.5 million U.S. residents between 2008 and 2023 to assess who takes up Medicaid coverage and who remains uninsured despite being eligible. Led by Rebecca Brooks Smith, a postdoctoral fellow in the Bloomberg School’s Department of Health Policy and Management, the study offers one of the most comprehensive national looks at how policy shifts have shaped Medicaid enrollment patterns.

“Our findings underscore how effective the ACA was at expanding coverage—but they also show who’s still being left behind,” said Smith. “Even with record-high take-up rates in 2023, it’s clear that procedural hurdles, geographic inequities, and policy decisions at the state level continue to limit access for many eligible Americans.”

Medicaid Take-Up Surged After ACA—And Held Steady in 2023 

Before the ACA’s major Medicaid expansions began in 2014, only 76.5% of eligible individuals were enrolled in the program. That figure jumped to 85% after the ACA and edged slightly to 86.5% in 2023—during the “unwinding” of the COVID-19 continuous enrollment provision that temporarily paused eligibility checks.

Despite concerns that the unwinding process would lead to widespread disenrollment, the study found that take-up remained stable or even increased in most categories. “That was a somewhat surprising and encouraging result,” Smith said. “It suggests that the investments in outreach and infrastructure, especially under the Biden administration, helped offset some of the risks we associate with large-scale policy transitions.”

However, the authors caution that the 2023 data may not capture the full scope of unwinding-related losses, as many states did not begin re-enrollment checks until mid-year and because the study relies on self-reported insurance status.

Persistent Gaps: Young Adults, Childless Adults, and Rural Residents 

While overall Medicaid participation increased, disparities remain stark. The research identified a number of groups which had consistently lower take-up rates even though they were eligible: 

  • Young Adults: Enrollment dropped dramatically at age 19, as many lost coverage when they aged out of childhood eligibility. Though the ACA helped narrow this gap, the drop-off remains a significant concern. 
  • Childless Adults: Once largely excluded from Medicaid, this group saw the most significant gains in take-up after the ACA. Still, in 2023, only 65% of eligible childless adults were enrolled—compared to nearly 94% of eligible children.
  • Rural Residents: Take-up was significantly lower in rural areas than urban ones, a gap that widened post-ACA. Limited access to enrollment assistance and fewer health care providers may contribute to this trend.
  • American Indian and Alaska Native Populations: These individuals had among the lowest take-up rates across all time periods studied—highlighting systemic barriers that outreach alone may not solve.

In contrast, the study found that eligible Black and Asian American individuals were more likely to enroll than white individuals and that take-up rates increased across all racial and ethnic groups post-ACA.

State Policy Still a Powerful Determinant 

Perhaps the most dramatic disparities stem from where people live. States that expanded Medicaid under the ACA consistently had higher participation rates than those that did not. In 2023, the take-up rate in expansion states was 88%, compared to just 78.7% in non-expansion states.

Even within eligibility groups, state policies—such as premiums or work requirements—were strongly associated with participation rates. For example, individuals in states that required any premium contribution were significantly less likely to enroll.

“The gap between the highest and lowest performing states is nearly 23 percentage points,” said Smith. “That’s a much wider margin than most individual factors like income or education. It illustrates how state policy decisions have an enormous influence not only on who is eligible but also on who ultimately enrolls.”

The study provides policymakers with evidence-based strategies to boost enrollment, increasing access to health care and strengthening the program, through tailored outreach to young adults and a smoother transition from childhood to adult Medicaid eligibility. The study also suggests reducing or eliminating premiums that may deter low-income individuals from signing up. It also emphasizes the importance of expanding outreach in rural areas and among American Indian and Alaska Native communities through community-based strategies. Finally, the study calls for safeguarding provisions of the Affordable Care Act and stabilizing the enrollment infrastructure.

These recommendations contrast with changes coming to Medicaid as a result of the 2025 Federal Budget Reconciliation Bill (One Big, Beautiful Bill Act-OBBBA). Over the next three years, the new legislation repeals incentives that encouraged ACA expansion, institutes work requirements that increase administrative burdens for individuals to enroll and remain enrolled, and increases cost-sharing by recipients, among other changes. Smith notes that these changes are expected to impact working adults and residents of rural areas, who are already less likely to enroll and more vulnerable to inadequate coverage and coverage loss.

“We have to make enrollment easier, more intuitive, and more trustworthy—especially for those who’ve historically been excluded or overlooked. Medicaid doesn’t work unless people actually enroll.” As the country braces for upcoming changes, which are phased in from January 2026 to January 2028, the authors stress the importance of continued monitoring. The lessons from the ACA era, they argue, should serve as a foundation—not a ceiling—for ensuring access to health coverage for all eligible Americans.