— For the 8 million people who persevered through all the technical travails in the new health insurance exchanges and managed to sign up for coverage in 2014, their policies will probably automatically renew come November when open enrollment begins.

Seems like good news after all the headaches consumers endured after the program’s launch last year. Except that renewing the same policy may not be the best choice. Many may end up paying far more than they need to and have policies that aren’t the best fit for their circumstances.

“[Automatic re-enrollment] could conceivably mean people will pay more in premiums unless they proactively take steps to comparison shop,” said Jenna Stento, a senior manager at Avalere Health, a health care research and consulting firm.

If you made a good choice last year, what could be so wrong about re-upping with the same plan?

Turns out plenty, particularly for those among the 87 percent of enrollees in health insurance exchange plans who received a federal subsidy to help pay for premiums. Understanding why that’s a problem isn’t easy, the result of complicated quirks in the Affordable Care Act, which established the exchanges in the first place.

Overall, premiums on the exchanges in 2015 may be a bit higher for most people, at least according to one analysis of proposed plans and rates in nine states. Avalere found that the average premiums for Silver plans will climb an average of 8 percent. (There are four grades of plans offered, starting with Bronze plans with the cheapest premiums, but higher deductibles and copays, and moving up to Silver, Gold and Platinum.)

Changing benchmarks

The Obama administration announced in June that consumers who bought their policies on the federal exchange would have them — and the amount of their subsidies — automatically renewed. It will be up to each state exchange whether to offer a similar automatic renewal. People whose level of income has changed would need to enroll again since it would affect the amount of their subsidies.

But consumers who automatically re-up with the plan they have could face steep and unexpected premiums and out-of-pocket costs, particularly if they received a federal subsidy.

Here’s why. The subsidy people receive is pegged to the second-lowest priced Silver plan, the so-called “benchmark plan,” meaning that the amount of a subsidy any individual receives, no matter which plan he or she selects, is based on how much they would receive if they picked that benchmark plan.

In a hypothetical example Avalere provides, “Sue,” a Maryland resident, enrolled in the 2014 benchmark Silver plan in her region — offered by CareFirst Blue Cross — which had a monthly premium of $214. Based on her income, Sue’s contribution toward her monthly premium was set at $58, so she qualified for a monthly federal subsidy of $156 to make up the difference. If Sue had chosen a plan with a higher premium, her federal subsidy would have remained fixed at $156 and she would have had to pay more out of her own pocket.

However, in 2015, according to Avalere’s analysis of early rate filings, CareFirst Blue Cross will no longer be the second-lowest Silver plan in Sue’s region but the ninth-lowest out of 18 Silver plans, meaning that it will lose its status as the benchmark plan. CareFirst’s new monthly premium is $267. The new benchmark Silver plan (the Silver plan with the second-lowest premium) will be the Kaiser Foundation Health Plan with a monthly premium of $231.

Sue’s contribution remains the same, but she will now qualify for a higher federal subsidy of $173 to make up the difference between her ability to pay $58 per month and the higher $231 monthly premium of the new benchmark.

If she automatically re-enrolls with CareFirst, however, she will have to cough up an additional $36 a month. By doing nothing, her out-of-pocket contribution will rise by 62 percent.

In another example, “Dave” enrolled in the benchmark Silver plan in Washington state, Group Health Cooperative, which had a monthly premium of $281. He received a federal subsidy of $85 each month, leaving him with a monthly out-of-pocket bill of $196.

In 2015, BridgeSpan Health will replace Group Health as the benchmark plan in Dave’s area, with a premium of $263 a month. Because of that lower premium, Dave will be entitled to only a $67 a month federal subsidy, leaving him again with a $196 monthly out-of-pocket expense if he switched to BridgeSpan. But if Dave sticks with Group Health, which hiked its premiums to $313, he will have to pay $246 each month out of his own pocket, a nearly $600 increase compared to last year.

It pays to look

This is not a theoretical wrinkle. Of the nine states whose 2015 premiums Avalere examined (Connecticut, Indiana, Maryland, Maine, Oregon, Rhode Island, Vermont, Virginia and Washington), all but Vermont appear headed for a new benchmark plan when open enrollment commences. Consumers who live in six of these states may have an unpleasant surprise when they see their bills if they let their policies automatically renew.

In Rhode Island and Virginia, the opposite may be true. Last year’s benchmark plans are expected to become the lowest-priced Silver plans, instead of the second-lowest.

Consumers renewing the 2014 benchmark plans in those two states could see their out-of-pocket premium costs decrease in 2015.

“There could be significant financial value to take a look at the site and see if there might be more affordable options for you, given the changes since last year,” Steno said.

Because of last year’s disastrous rollout, most exchanges will have modest ambitions for the second enrollment period. Offering consumers a smooth enrollment experience is the goal of most exchanges. But a smooth experience won’t necessarily be enough to guarantee landing the best policy.