But even with the gains under the health-care law, 25.2 percent of adults who bought insurance on their own last year said they went without medical tests or treatments, prescription drugs or doctor visits because of cost. Because most adults who buy insurance on their own do not have dental care as part of their health coverage, the ability to see a dentist was not included in the main part of the report.
But when dental care is added to the mix, it becomes the most common type of care that adults skip because of its cost.
Hardest hit were lower to middle-income adults. That's someone who earned from $16,200 to $29,199 last year, or a family of three earning from $27,400 to $49,499. Almost one out of three of these adults said they went without needed medical care because the out-of-pocket cost was too high.
"The key culprit as to why people have been unable to afford medical care despite having year-round coverage is high deductibles," said Ron Pollack, executive director of Families USA.
A deductible is the amount consumers owe for covered health-care services before their insurance plan begins to pay. The report defines high deductibles as $1,500 or more per person.
More than half of adults had deductibles of $1,500 or more and 30 percent had "exceedingly high deductibles" of $3,000 or more, the report found.
Health insurance has been getting less and less generous in recent years for many Americans, experts say, making it difficult for them to pay for care even when they have insurance, a trend that predates the Affordable Care Act.
The health law has led to more people getting insurance, and provides for financial help in the exchanges for those with low incomes. But for many of those newly insured under the law, affording care is still a challenge because deductibles and co-pays are often quite high, experts say.
Many people who enrolled in coverage through the exchanges picked health plans with lower premiums, such as bronze and silver plans. (There are five categories of plans and they differ based on how much consumers and insurers share the costs of care. In a bronze plan, the insurance company covers, on average, 60 percent of health care costs; in a Silver plan, roughly 70 percent).
The estimated average deductible of silver plans in 2014 was between $2,267 and $3,030, the report said.
Lydia Mitts, a co-author of the report, said insurers could reconfigure their plans to be more affordable. On Connecticut's health insurance exchange, for example, all insurers are required to offer a silver plan that exempts basic outpatient services, such as doctor visits, lab work and prescriptions for generic drugs, from the $3,000 deductible, she said. Instead, consumers have a co-pay of $30 to see a primary care doctor and a co-pay of $10 for generic drug prescriptions.
"It can be a model for insurers," she said.
The numbers in the report come from data collected by the Urban Institute, which surveys a nationally representative sample of about 7,500 non-elderly adults every quarter. The sample in this analysis includes 1,229 such adults with incomes above 138 percent of the federal poverty level.