Overall, health care costs have increased at historically low rates in recent years, said Matthew Fiedler, a health economist at the Brookings Institution. “We’ve got lots of indicators, across a constellation, that the health care trend is pretty low,” he said.

While employers credit their efforts to slow down costs, others, including Mr. Fiedler, say some of the changes enacted under the Affordable Care Act have also contributed. The federal law reduced what Medicare pays for care, which allows private payers to strike better bargains, he said, and the government has been encouraging experiments in how to pay doctors and hospitals in new ways that may reduce spending.

Even the deductibles people pay toward their own medical bills, which have gone up steadily in recent years, seem to be holding steady. Deductibles rose only slightly this year, averaging $1,505 for a single person, according to Kaiser.

While employers have relied on steeper deductibles to lower their own costs, companies are recognizing that they have reached the limits of what they can ask their workers to pay, said Michael Thompson, the chief executive of the National Alliance of Healthcare Purchaser Coalitions, which represents employers. “We’re running out of runway to keep cost-shifting to employees,” he said.

But people remain confused about how the turmoil in the individual market affects them, even when they get their coverage through an employer, Mr. Altman said. In a recent Kaiser poll, six out of 10 Americans worried that the higher rates being charged in the A.C.A. markets would negatively affect them, he said.

The two markets are distinct, and the groups of people being covered are “like night and day,” Mr. Altman said. The individual market has a large portion of people who need expensive medical care, which has led to sharply higher prices some areas. The large employer market can spread the costs of expensive care more easily over the greater numbers of people that work for large companies.

Small businesses, however, can’t spread their medical costs over a large work force. Premiums “have gone up double digits up here,” said Martin Dole, the controller for Gateway Motors, a car dealership in White River Junction, Vt., which covers 28 people.