A Look at ACA Coverage through the Marketplaces and Medicaid Expansion Ahead of Potential Policy Changes

The Affordable Care Act (ACA) expanded health insurance coverage by extending Medicaid coverage to nearly all adults with incomes up to 138% of the federal poverty level (FPL) ($20,783 for a single individual in 2024) and by creating new health insurance Marketplaces through which individuals can purchase private insurance coverage with financial help to afford premiums and cost-sharing. Marketplace subsidies are available for individuals not eligible for Medicaid with incomes above 100% FPL. The Medicaid expansion was originally mandatory for states, but expansion became effectively optional after a Supreme Court decision in 2012. States can opt to provide more affordable coverage to individuals who would otherwise be eligible for Marketplace coverage with incomes between 133% and 200% FPL through a Basic Health Program (BHP). In 2024 Minnesota had a BHP plan, Oregon newly implemented a BHP on July 1, 2024, and New York had a BHP until April 2024 when it transitioned to provide the same coverage to individuals with incomes up to 250% FPL through the state’s Essential Plan (EP).

In total, 2024 ACA enrollment (including Marketplace, Medicaid expansion, and BHP) reached 44 million, or 16.4% of the nonelderly U.S. population. In 2024, Marketplace enrollment hit a new record high, of 21.4 million people (almost double the 11 million people enrolled in 2020), Medicaid expansion enrollment was 21.3 million (a 41% increase from 2020), and BHP enrollment in 2024 was 1.3 million (up from 880,000 in 2020).

Marketplace growth since 2020 can be largely attributed to enhanced subsidies made available by the American Rescue Plan Act (ARPA) in 2021 and renewed through 2025 under the Inflation Reduction Act (IRA). These enhanced subsidies significantly reduced premium payments across the board for ACA Marketplace enrollees – including $0 monthly premiums for enrollees with incomes up to 150% FPL – and made some middle-income people who had previously been priced out of coverage newly eligible for financial assistance. Medicaid expansion enrollment increased due to seven states newly implementing expansion in 2020 or later and adoption of the continuous enrollment provision, a pandemic-era policy that prohibited states from disenrolling people from Medicaid in exchange for enhanced federal funding. Even with the unwinding of the continuous enrollment provision starting April 1, 2023, enrollment in the Medicaid expansion today is higher than it was in 2020.

The uninsured rate hit an historic low in 2023 as coverage through the ACA and Medicaid increased, but these coverage gains may not last for long. If enhanced subsidies are not renewed by Congress and are instead allowed to expire at the end of 2025, ACA enrollee premium payments are expected to increase by over 75% on average, and the Congressional Budget Office (CBO) estimates that the number of people who are uninsured will increase by 3.8 million, on average, in each year over the 2026-2034 period. In addition, potential Congressional efforts to lower the Medicaid expansion match rate from the current 90% rate could reduce federal spending but would shift costs to states and likely result in decisions by many states to terminate coverage. About 4.3 million Medicaid expansion enrollees live in states with some type of trigger law that would end Medicaid expansion or require review of expansion coverage to mitigate increases in state costs if federal funding for the expansion is reduced. There is also potential for deeper cuts to the ACA and Medicaid to help offset increases in the deficit if expiring tax cuts are extended.

While 1 in 6 nonelderly people in the U.S. had some form of ACA coverage in 2024, there was significant variation across states. More than 1 in 5 nonelderly people in seven states (Louisiana, Oregon, Florida, New York, California, New Mexico, and Vermont) and the District of Columbia had ACA coverage through Medicaid expansion, Marketplace, or BHP in 2024. Meanwhile, fewer than 1 in 10 nonelderly residents of five states (Alabama, Kansas, Tennessee, Wisconsin, and Wyoming) had coverage through one of these three ACA programs (Figure 1). With the exception of Florida, the states with the largest ACA enrollment as a share of population had adopted the Medicaid expansion. The five states with the lowest share of enrollment were Medicaid non-expansion states.

From 2020 to 2024, total enrollment in ACA programs (Medicaid expansion, Marketplace, and Basic Health Plan) increased by nearly 60%, with the largest increase among Marketplace enrollees. Growth in Marketplace enrollment from 2020 can be largely attributed to the temporary enhanced subsidies that were made available in 2021 and extended through 2025. Marketplace enrollment growth was greatest among states that have not expanded Medicaid. Meanwhile, Medicaid expansion enrollment similarly increased due to more states implementing expansion (seven states — Idaho, Missouri, Nebraska, North Carolina, Oklahoma, South Dakota, and Utah — implemented Medicaid expansion during or after 2020), and because of the pause in disenrollments from the continuous enrollment provision. Even with the unwinding of the Medicaid continuous enrollment provision that was still in play through March 2024, enrollment in Medicaid expansion is currently higher than it was in 2020. The number of Marketplace enrollees increased by 10 million people nationally, almost doubling, between 2020 and 2024, and the number of Medicaid expansion enrollees increased by 6.2 million people. In 2024, Marketplace consumers made up 49% of all people enrolled in ACA coverage compared to 42% in 2020 (Figure 2).

From 2020 to 2024, the rate of growth in ACA enrollment varied widely by state, more than doubling in some states while changing very little in others. Enrollment across the three ACA programs more than doubled from 2020 to 2024 in twelve states: Missouri (243%), Oklahoma (227%), Texas (212%), Mississippi (190%), North Carolina (185%), Georgia (181%), Tennessee (177%), South Carolina (167%), South Dakota (155%), Alabama (141%), Florida (120%), and Nebraska (113%, Figure 3). Meanwhile, other states saw less than 20% growth over those four years: Washington (19%), Rhode Island (18%), Kentucky (17%), Colorado (17%), the District of Columbia (16%), Montana (14%), New Mexico (11%), and Massachusetts (10%).

Of the ten states with the largest increase in ACA program enrollment from 2020 to 2024, all were won by President Trump in the 2024 election, and none had expanded Medicaid before 2020. In non-expansion states, individuals with incomes between 100% and 138% FPL are eligible for subsidized Marketplace coverage, and with the enhanced subsidies making the coverage more affordable by providing coverage with $0 premiums, more people enrolled. All non-expansion states, except Wisconsin, and all states that adopted Medicaid expansion in 2020 or later, except Idaho, had increases in ACA enrollment that exceeded the national increase of 61%. (Wisconsin Medicaid eligibility extends to 100% FPL so there is no coverage gap.) Meanwhile, many of the states with lower enrollment growth over the last four years have long embraced the ACA (adopting Medicaid expansion early on and creating their own state-based Marketplaces), so they started out with relatively high shares of their populations already enrolled in ACA coverage in 2020 (Table 1).