Dan Lopez rarely gets sick and hasn’t been to a doctor in 10 years, so buying health insurance feels like a waste of money.

Even after the federal health overhaul takes full effect next year, the 24-year-old said he will probably decide to pay the $100 penalty for those who skirt the law’s requirement that all Americans purchase coverage.

“I don’t feel I should pay for something I don’t use,” said the Milwaukee resident, who makes about $48,000 a year working two part-time jobs.

Because he makes too much to qualify for government subsidies, Lopez would pay a premium of about $3,000 a year if he chose to buy health insurance.

“I shouldn’t be penalized for having good health,” he said.

Persuading young, healthy adults such as Lopez to buy insurance under the Affordable Care Act is becoming a major concern for insurance companies as they scramble to comply with the law, which prohibits them from denying coverage because of pre-existing conditions and limits what they can charge to older policy holders.

Experts warn a lot of these so-called “young invincibles” could opt to pay the fine instead of spending hundreds or thousands of dollars each year on insurance premiums. If enough young adults avoid the new insurance marketplace, it could throw off the entire equilibrium of the Affordable Care Act. Insurers are betting on the business of that group to offset the higher costs they will incur for older, sicker beneficiaries.

The nonpartisan Congressional Budget Office estimates that about six million people of various ages will pay the tax penalty for not having insurance in 2014, the first year the law championed by President Barack Obama will be fully implemented.

It’s hard to estimate how many of those will be the young and healthy adults insurers are trying to reach, but that subgroup makes up a very small portion of the overall market. Even though it’s small, experts say it could be enough to throw the system’s financing off-kilter.

About 3 million 18-24 year-olds in the U.S. currently purchase their own insurance. Many pay high prices for scant benefits, with high deductibles and co-pays because they make too much to qualify for Medicaid and have no coverage options from their employers or parents. The Urban Institute estimates that the majority of adults in their 20s will qualify for government subsidies under the Affordable Care Act.

Premium hikes could be a disincentive for young people weighing their options. Premiums for people aged 21 to 29 with single coverage who are not eligible for government subsidies would increase by 42 percent under the law, according to an analysis by actuaries at the consulting firm Oliver Wyman. By comparison, an adult in his or her early 60s who would see about a 1 percent average increase in premiums under new federal health rules.

Insurers including America’s Health Insurance Plans and The Blue Cross and Blue Shield Association recently wrote to federal health officials warning that they feared low enrollment by young adults and proposed beefed up penalties for opting out. Insurers worry the $100 penalty might not be a strong enough deterrent. The penalties jump to $695 or 2.5 percent of taxable income – whichever is more – by 2016.

“The key to keeping health care affordable is you really want to balance the pool, where you have enough young and healthy people to balance off the care of the older, sicker people who are likely to utilize much more health care services,” said Justine Handelman, the Blue Cross and Blue Shield Association’s vice president for legislative and regulatory policy.