It will offer exchange plans for the first time in Florida, Illinois, Michigan and North Carolina.

“We think the second vintage will be better,” Stephen Hemsley, United’s CEO, said on a call with investors this month. “The third vintage will be better after that.”

UnitedHealth officials said they expect to earn profits on their exchange business next year, though they cautioned the likely margin will be less than the 3% to 5% level they expect in the long run.

Like UnitedHealth, most publicly traded insurers took a cautious approach in 2014 to the exchanges established by the Patient Protection and Affordable Care Act. That’s partly because they faced an enrollment pool that was unpredictable in terms of age and health status. In addition, the individual market has made up only a small portion of their total business. The notable exception was WellPoint, the Blue Cross and Blue Shield-affiliated company, which competed for exchange customers in all 14 states where it does business.

But UnitedHealth and other publicly traded insurers are expanding their exchange presence for the 2015 open enrollment period, which lasts three months. Experts say insurers recognize the shift toward a more individual consumer-oriented market, with the likelihood that an increasing number of employers will have their workers shop for plans on public and private exchanges. In addition, insurers expect a more balanced pool of healthier and sicker enrollees as the exchange population grows larger and the tax penalties increase for not buying coverage.

Cigna Corp. plans to compete in eight states, three more than in 2014. Humana and Aetna each are adding one state, competing in 15 and 17 states, respectively. Other insurers are retooling their plans and rates to attract consumers. In some cases, they are narrowing their provider networks and reducing premiums to entice customers who have shown a strong preference for lower rates even if that means less provider choice and higher deductibles.

One reason UnitedHealth and other large insurers are expanding their exchange participation is they risk getting squeezed out of the growing individual and small-group exchange market if they stay on the sidelines too long, said David Dranove, a professor of health industry management at Northwestern University. According to HHS, 7.3 million individuals signed up for 2014 coverage through the federal and state exchanges. The Congressional Budget Office estimated that number will swell to 13 million in 2015.

Dranove said the risk for latecomers is that consumers tend to stick to the health plans they are in. “We’ve learned from Medicare Advantage, from Medicare Part D and from private insurance that there’s a huge amount of enrollment inertia,” Dranove said. “If you wait too long, everybody’s going to be locked into their insurers.”

But even if UnitedHealth and other publicly traded insurers are successful at securing a larger footprint in the exchanges, that will represent a small amount of their overall business. An analysis by Barclays found that if UnitedHealth attracts 10% of exchange customers in the 24 states where it plans to compete and that business turns a 3% profit, it would boost earnings per share by only 2%.

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Insurers that took a conservative approach to the exchanges for 2014 may be at a competitive disadvantage in the coming open enrollment because current exchange plan members who take no action will be automatically re-enrolled in the same plan (or the closest comparable product offered by their insurer) for 2015. “While that is a big positive for incumbents, it can be a big negative for new entrants like United, as the total market available to new entrants will be much smaller than otherwise would have been the case,” Citi Research analysts wrote.

The expanded participation of the country’s largest commercial insurers has contributed to increased competition on the exchanges. Last month, HHS announced that in 44 states where complete data were available, 25% more insurers will be selling plans on the exchanges for 2015. That includes nine states where there will be at least three new companies offering plans. The only state where competition decreased is California, which still will have 10 insurers selling exchange products.

HHS Secretary Sylvia Mathews Burwell pointed to the increased competition as a sign that the new marketplaces are thriving despite the severe technological problems that plagued HealthCare.gov initially and continued to hobble some state-run exchanges throughout open enrollment.

But Mark Pauly, a healthcare economist at the University of Pennsylvania, cautioned that having more insurers participating is not necessarily a sign that the exchanges are succeeding. For the first three years, insurers can rely on the federal risk-corridor and other mechanisms established by the healthcare reform law to protect them from significant losses if they attract a sicker, more-expensive enrollment population than they anticipated. Humana, for example, has predicted that it will receive between $575 million and $775 million through those programs for 2014 Obamacare customers. Those risk protections, plus the insurance industry’s desire to be seen as supportive of the reform law, are likely enticing the publicly traded insurers to expand their participation in the exchanges, he said.

“It’s very much in an infant stage,” Pauly said. “A lot of people are helping to care for this baby. The real test will be when it heads off to kindergarten.”

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Insurers expect the risk pool to continue to improve, lessening the need for such risk-protection mechanisms.

The emergence of UnitedHealth as a bigger exchange player is likely good news for consumers. The second-cheapest silver plan in states that used the federal exchange would have been 5.4% cheaper in 2014 if UnitedHealth had been competing, according to a study conducted by Northwestern University and Massachusetts Institute of Technology researchers that will be published in the American Journal of Health Economics.

The rate for the second-cheapest silver plan in each market is important because it’s used as the benchmark for calculating the amount of federal premium subsidies.

Indianapolis-based WellPoint gained lots of members as a result of its aggressive entry into the exchanges in 2014, adding 769,000 customers during the first six months of the year, according to company officials. That was more than 10% of all exchange enrollment nationally.

Rob Ruiz-Moss, WellPoint’s vice president for exchange strategy and execution, said his company’s experience validated the decision to participate broadly in the exchanges. The risk pool in terms of age and health status generally met WellPoint’s expectations, Ruiz-Moss said. But because so many signups poured in during the final frenzied weeks of the open enrollment period, the company’s actuaries had only a few weeks, and not much demographic data, for calculating 2015 rates before WellPoint had to file those new rates.

“There’s still a lot of young business on the books, but at this point, we don’t see any large-scale concerns,” he said. “We don’t see any red flags.”

WellPoint is retooling its website to make it easier for individual-market consumers to sign up for coverage outside of the exchanges. It’s also bolstering its Spanish-language outreach and focusing more on mobile marketing.

Aetna signed up nearly 600,000 exchange customers during the first open enrollment. Roughly two-thirds of those new customers selected a plan during the last two months of the enrollment period, meaning Aetna had little utilization data on which to base its 2015 rates. Through attrition, the Hartford, Conn.-based company expects to end the year with roughly 500,000 customers—a 17% drop-off rate. That attrition is fairly typical for what insurers are seeing.

Cigna CEO David Cordani told investors in July that during the first quarter of the year the company’s exchange customers skewed older and more expensive than anticipated. But the risk profile improved during the second quarter as enrollment accelerated and more young people signed up. “We’ve positioned this business to be manageable,” Cordani said. “We didn’t expect to make money. We’re not making money.”

Molina Healthcare, which primarily has been in the Medicaid managed-care business, opted to compete for 2014 in exchanges in nine of the 11 states where it does Medicaid business. The Long Beach, Calif.-based company signed up roughly 23,000 exchange customers. More than 10,000 of those new members came through the California exchange, where the insurer competed in four of the state’s 19 regions. The company’s market share in each region ranged from less than 1% to 6.4%.

Lisa Rubino, a senior vice president at Molina, said enrollment was below expectations for the first year but that her company is not discouraged. It again will be competing in nine states for 2015 customers and is adding counties in some states. In some exchange markets, Molina is adding lower-priced bronze plans or expanding its provider networks to compete more effectively.

Molina’s biggest change for the next open-enrollment window will be in pricing, offering lower rates in most states, Rubino said. In Washington state, where Molina captured just over 2,000 customers in 2014, the company will hold its premiums flat for 2015. In California, Molina’s rate increases will range from an average of 0.6% in one region to 3.1% in another.

Not all publicly traded insurers are expanding their exchange footprint for 2015. Woodland Hills, Calif.-based Health Net competed in three states—Arizona, California and Oregon—in 2014. In California, Health Net captured roughly 20% of the market, compared with 3% before the establishment of the exchange. In Arizona, Health Net went from virtually no members in the individual market to 30% of that market at the end of June.

Meanwhile, Health Net is exiting the Oregon exchange market because of low market penetration there. That will enable the company to concentrate on the California and Arizona exchange markets, said Jennifer Moore, Health Net’s vice president for individual markets.

One surprise in the first year was that 15% to 20% of new Health Net members didn’t pay their premiums, Moore said. To figure out why, Health Net conducted focus groups with those consumers who signed up but didn’t pay.

In response to the feedback, Health Net stepped up its communications with members immediately after they signed up for a plan to encourage them to make payments. The company also redesigned its invoices to make it clearer they were bills.

Now Health Net intends to make five contacts with all 2014 customers about renewing their plans, including sending a personalized video appeal to those customers who provided e-mail addresses. The company also aims to expand its outreach to Hispanic residents, featuring Spanish-language radio ads, billboards and hand sanitizers given out in grocery stores.

“We’re very pleased with the outcome for year one,” Moore said. “We knew it was going to be a pretty bumpy implementation.”

Follow Paul Demko on Twitter: @MHpdemko