But the tally underscores a looming risk to Obamacare from a pending Supreme Court case, which threatens to eliminate the financial help that most people in ACA plans get in buying their plans.
About 85 percent—or almost 8.7 million—of all of the paying customers nationally qualified for federal tax credits that offset the price of their monthly premiums. Those subsidies worth an average of $272 per month are available to people with low or moderate incomes.
Most of the subsidized customers, 6.4 million people, have subsidized coverage through 34 of the states served by the federal exchange HealthCare.gov.
The Supreme Court is set to rule this month on whether financial aid to customers in those states is illegal. Plaintiffs in the case known as King v. Burwell claim the Affordable Care Act as written prohibits subsidies being granted to anyone other than customers of a state-established exchange.
If the Supreme Court ruled for the plaintiffs, it would end about $1.8 billion worth of financial assistance per month to customers in the affected states.
The ten states in the U.S. with the highest rates of customers receiving subsidies—above 90 percent in each state—are all served by HealthCare.gov. according to data released Tuesday.
Additionally, 60 percent of all enrollees in the affected states also receive so-called cost-sharing reductions, financial aid to offset the out-of-pocket expenses from deductibles, co-payments and co-insurance that customers have to personally pay when they get medical treatment. Those cost-sharing reductions, which are given to premium subsidy recipients who earn less than 2.5 times the poverty level, are also at risk from the King v. Burwell case.
"A victory for the plaintiffs in King v. Burwell could destabilize insurance markets in two-thirds of the states," said Obamacare expert Timothy Jost, a health law professor at Washington & Lee University.
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"Virtually all of the federal exchange enrollees receiving premium tax credits would be unable to afford coverage without those credits. Healthy enrollees would likely drop coverage, leaving a much higher cost group of enrollees behind. Insurers would have to raise premiums to cover them, making coverage unaffordable for all their enrollees."
The HealthCare.gov states with the highest numbers of subsidized customers are Florida with 1.32 million people, Texas with about 832,000 people, and North Carolina, with almost 459,000 subsidy-aided Obamacare customers.
Experts have predicted that up to 8.2 million people in HealthCare.gov states would drop their insurance coverage next year if the subsidies are ended. Those people would include non-subsidized customers whose premiums would become too pricey.
Ceci Connolly, Health Research Institute leader at PricewaterhouseCoopers, said "The numbers once again underscore the power of the subsidies—without them, far fewer Americans would have health insurance coverage."
"If the subsidies disappear, health-care providers face financial difficulties as well since we know that the uninsured often seek care at an emergency department regardless of whether they can pay," Connolly said. "Hospitals are worried about uncompensated care debt rising again to pre-ACA levels."
The 2.3 million people who received federal tax credits to help pay for insurance plans purchased on exchanges established by individual states would not be affected by the high court ruling. The lowest rate of subsidized paid Obamacare customers are seen among six states and the District of Columbia, which all run their own exchange.