Enough insurers are planning to sell coverage on the Affordable Care Act’s insurance exchanges next year to keep them working — if only barely — in most parts of the country.

Competition in many markets has dwindled to one insurer — or none in some cases — and another round of steep price hikes is expected to squeeze consumers who don’t receive big income-based tax credits to help pay their bill.

“What we’re seeing is a deterioration in these markets, but the markets haven’t imploded, they haven’t gone into a rapid downward decline,” said Dan Mendelson, president of the consulting firm Avalere.

Health insurers had until Wednesday to declare whether they planned to sell coverage next year on exchanges in most states. Actual participation and final rates won’t be set until late summer or closer to the Nov. 1 start of enrollment for next year’s coverage.

Early plans filed by many insurers for next year include premium increases well over 20 percent, and Avalere expects more than 40 percent of U.S. counties to have only one insurer selling coverage on the exchange, the only place where shoppers can get tax credits to help pay the bill. Some counties in Missouri, Ohio, Indiana and Washington will have none if another insurer fails to step in.

The early picture for 2018 looks much like it did for previous years: Insurers are retreating from some markets or charging a lot more to stay in others.

The Blue Cross-Blue Shield insurer Anthem said Wednesday that it will leave exchanges in Wisconsin and its home state of Indiana. This comes a few weeks after the nation’s second-largest insurer also said it was pulling out of Ohio’s exchange.

The health insurer Medica recently said it will return to Iowa next year, a move that saves most of that state’s counties from having no exchange options. But Medica anticipates hiking rates more than 43 percent on average.

Nationwide, prices for individual insurance could rise between 28 and 40 percent on average, according to a prediction by Oliver Wyman Actuarial Consulting.

Most of that expected increase reflects concerns over how President Donald Trump’s administration will manage the program, the consulting firm said. It may stop enforcing a mandate that most Americans buy coverage or it may halt cost-sharing payments that soften expenses for people with modest incomes. The mandate is seen as crucial to encouraging healthy people to enroll and balance the costs an insurer incurs from people who use their insurance.

Trump and other administration officials have said that the Affordable Care Act is collapsing, and they are trying to marshal a replacement plan through Congress. The Senate is weighing a new plan and may vote on it next week.

Insurers have been gouged by steep losses on this kind of coverage since they started paying claims in 2014, and big companies like Humana, Aetna and UnitedHealth Group have either left entirely or retreated to just a few states. Those that remain have been raising premiums by 10 percent or more since.

Heading into 2018, insurers are still worried about attracting enough healthy people to balance claims from the sick. But repeated price hikes can fuel that problem because they make insurance less attractive to healthy people.

Despite all those concerns, more than two dozen insurers have said they are making plans to continue selling coverage on the exchanges. Some, like Centene and Oscar are expanding into new markets.

These insurers have decided to stay or expand despite the uncertainty for a few reasons. Some, nonprofit Blue Cross-Blue Shield plans in particular, have spent decades in their markets and are reluctant to end such long-standing presences. They see themselves as the “insurer of last resort,” which means they make sure a market has at least one coverage option.

Others want to protect investments they have made into setting up networks of providers, hoping they can eventually make money. And others have already found ways to make the business profitable.

Centene, for instance, uses what it has learned managing state and federally funded Medicaid program for the poor to market insurance on the exchanges to low-income customers in areas where it has already formed networks of providers for that business.

Insurers also get an assist from the government. They know that the income-based tax credits that pay most of the insurance bill for some customers shield those people from big price hikes, said Robert Laszewski, a health care consultant and former insurance executive. That means companies can raise their premiums high enough to avoid losses and not worry about hurting the individual or family with the coverage.

“The taxpayer is going to pay for it,” Laszewski said.