Patient Protection and Affordable Care Act

In 2010, 48.6 million people in the United States had no health insurance, 16.0 percent of the population, and among adults aged 18 to 64 the figure was 22.3 percent. Private insurers could refuse to cover a person's existing illnesses and could cap the total they would ever pay out. H.R. 3590 passed the Senate in amended form in December 2009, the House accepted the Senate version on 21 March 2010, and the bill became law on 23 March.

Some changes arrived within six months. Plans could no longer set lifetime dollar limits on benefits, children under 19 could not be denied coverage of preexisting conditions, and plans that covered dependents had to let young adults stay on a parent's plan until age 26. The larger changes began with plan years starting on 1 January 2014: the ban on preexisting-condition exclusions reached adults, most people had to carry coverage or pay a shared responsibility payment, refundable tax credits helped buyers of marketplace plans, and Medicaid was to cover adults with incomes up to 133 percent of the federal poverty level.

Twenty-six states, several individuals and the National Federation of Independent Business sued. On 28 June 2012 the Supreme Court upheld the coverage requirement, with Chief Justice Roberts writing that it could stand under Congress's power to tax. The Court also held that the federal government could not take away a state's existing Medicaid funds for refusing the expansion. That left each state a real choice about whether to expand, and the rest of the law stood.

Enrollment in the marketplaces opened in October 2013. HHS analysts estimated that by February 2016 the law had brought coverage to 20.0 million adults, including 2.3 million people aged 19 to 25 who stayed on a parent's plan before 2014, and that the uninsured rate among adults aged 18 to 64 had fallen from 20.3 to 11.5 percent since October 2013. In the first three months of 2017 the National Health Interview Survey counted 28.1 million uninsured people, 8.8 percent of the population and 20.5 million fewer than in 2010. That quarter, 9.4 million adults had private plans bought through the marketplaces.