Amid the challenges of adulthood, there is one rite of passage unique to the United States: the need to find your own health insurance by the time you turn 26.

That is the age at which the Affordable Care Act declares that young adults generally have to get off their family’s plan and figure out their own coverage themselves.

When the A.C.A. was voted into law in 2010, its so-called dependent coverage expansion was immediately effective, guaranteeing health insurance to millions of young Americans up to age 26 who would otherwise have not had coverage.

But for years, Republicans have whittled away at the infrastructure of the original law. Long gone is the requirement to buy insurance. Plans sold in the online insurance marketplaces have no stringent quality standards. Costs keep rising, and eligibility requirements and subsidies are a moving target.

The erosion of the law has now created an “insurance cliff” for Americans who are turning 26 and don’t have a job that provides medical coverage.

Some, scared off by the complexity of picking a policy and by the price tags, tumble over the edge and go without insurance, in a health system where the rate for an emergency room visit can be thousands, if not tens of thousands, of dollars.

Today, an estimated 15 percent of 26-year-olds go uninsured, which, according to an analysis by the health research group KFF, is the highest rate among Americans of any age.

If they qualify, young adults can sign up for Medicaid, the federal and state program for low-income Americans, in most but not all states.

But many buy cheap subpar insurance that leaves them with insurmountable debt following a medical crisis. Others choose plans with extremely limited networks, losing access to their longtime doctors and medicines.

Often they find those policies online, in what has become a dizzyingly complicated system of government-regulated insurance marketplaces.They vary in quality from state to state; some are far better than others.

But they generally offer few easily identifiable, affordable and workable choices.

“The good news is that the A.C.A. gave young people more options,” said Karen Pollitz, who directed consumer information and insurance oversight at the Department of Health and Human Services during the Obama administration.

“The bad news is the good stuff is hidden in a minefield of really bad options that’ll leave you broke if you get sick.”

Publicly funded counselors called “navigators” or “assisters” can help insurance seekers choose a plan. But those programs vary by state, and often customers don’t realize that the help is available. The Trump administration has cut funding to publicize and operate those navigator programs.

In addition, changes to Medicaid eligibility in the policy bill passed by Congress in July could mean that millions more enrollees lose their insurance, according to the Congressional Budget Office.

Those changes threaten the very viability of the online marketplaces, which currently provide insurance to 24 million Americans.

In dozens of interviews, young adults described the unsettling and devastating consequences of having inadequate insurance, or no insurance at all.

Damien Phillips, 26, a reporter at a West Virginia newspaper, considered joining the Navy to get insurance as his 26th birthday approached. Instead, he felt he “didn’t make enough to justify having health insurance” and has reluctantly gone without it.

When Ethan Evans, a 27-year-old aspiring actor in Chicago who works in retail, fell off his parents’ plan and temporarily signed up for Medicaid, diminished mental health coverage meant cutting back on visits to his longtime therapist.

Representative Maxwell Frost, Democrat of Florida, the first Gen Z member of Congress, was able to quit his job and run for office at 25 only because he could stay on his mother’s plan until he turned 26, he said.

Now 28, he is insured through his federal job.

“The A.C.A. was groundbreaking legislation, including the idea that every American needs health care,” he said.

“But there are pitfalls, and one of them is that when young adults turn 26, they fall into this abyss.”

Why 26?

Back in 2010, the decision to make 26 the cutoff age for staying on a parent’s insurance was “kind of arbitrary,” recalled Nancy-Ann DeParle, deputy chief of staff for policy in the Obama White House.

“My kids were young, and I was trying to imagine when my child would be an adult.”

Before that time, children were often kicked off family plans at much younger ages, typically 18.

The Obama administration’s idea was that by 26, young adults were most likely settling into careers and jobs with insurance. But if they still didn’t have access to job-based insurance, Medicaid and the online marketplaces would offer alternatives, the thinking went.

But over the years, the courts, Congress and the first Trump administration eviscerated provisions of the A.C.A. By 2022, a shopper on the marketplace run by the federal government had more than 100 choices, many of which included expensive trade-offs, presented in a way that made comparisons difficult without spreadsheets.

Jack Galanty, 26, a freelance designer in Los Angeles, tried to plan ahead of his 26th birthday and sought coverage on the California insurance marketplace that would ensure treatment for his mild cerebral palsy and for H.I.V. prevention.

“You’re scrolling for what feels like years, looking at 450 little slides, at the little bars, and trying to remember, ‘Was the one I liked number 12 or 13?’” he recalled. “It feels like it’s nearly impossible to make a good choice in this scenario.”

Out-of-pocket expenses have soared. Complex plans in the lightly regulated marketplaces featured rising premiums, high deductibles and requirements that patients pay a significant portion of the cost of care, often 20 percent — a charge known as coinsurance.

More than half of Americans aged 18 to 29 have incurred medical debt in the past five years, a KFF Health News data investigation found. Few have the reserves to pay it off.

The networks of doctors to choose from in these plans are often so limited that an insured person struggles to get timely appointments. It can even be hard to find the official websites amid an explosion of look-alikes operated by commercial brokers.

Sharing her contact information with one site that appeared legitimate left Lydia Herne, a social media producer in Brooklyn, “drowning” in texts and phone calls offering plans of uncertain and unregulated quality. “It never ends,” said Ms. Herne, 27.

Young Invincibles, an advocacy group representing young adults, runs its own “navigator” program to help young people choose health insurance plans.

“We hear the frustration,” said Martha Sanchez, who was until recently the group’s director of health policy and advocacy. “Twenty-six-year-olds have had negative experiences in a process that’s become really complex. Many throw up their hands.”

Elizabeth Mathis, 29, and Evan Pack, 30, a married couple in Salt Lake City, turned to the marketplaces two years ago, after Mr. Pack went uninsured for a “really scary” year after he turned 26.

“Every time he got in the car, I thought, ‘What if?’” Ms. Mathis said.

The couple pays more than $200 a month for a high-deductible health plan backed by a federal subsidy (the kind that is set to expire next year). It’s a significant expense, but they wanted to be certain that they had access to contraception and an antidepressant.

But last year, Mr. Pack suffered serious eye problems and underwent an emergency appendectomy. Their plan left them $9,000 in debt, for medical care billed at over $20,000.

“Technically, we gambled in the right direction,” Ms. Mathis said. “But I don’t feel like we’ve won.”

The Affordability Problem

The A.C.A. was supposed to help consumers find affordable, high-quality plans online. The legislation also tried to expand Medicaid programs, which are administered by states, as a way to provide health insurance to low-income Americans.

But the Supreme Court ruled in 2012 that states could not be forced to expand Medicaid. Ten states, led mostly by Republicans, have not done so, leaving up to 1.5 million Americans, who could have qualified for coverage, without insurance.

Even where Medicaid is available to 26-year-olds, the transition has often proved precarious.

Madeline Nelkin of New Jersey, who was studying social work, applied for Medicaid coverage before her 26th birthday in April 2024 because her university’s insurance premiums were more than $5,000 annually.

But it was September before her Medicaid coverage kicked in, leaving her uninsured while she fought a chest infection over the summer.

“People tell you to think ahead, but I didn’t think that meant six months,” she said.

When Megan Hughes, 27, of Hartland, Me., hit the cliff, she went without. An aide for children with developmental delays, she has a thyroid condition and polycystic ovary syndrome.

She looked for a health care plan but found it hard to understand the marketplace. (She didn’t know there were navigators who could help.) Now she can’t afford her medicine or see her endocrinologist.

“I’m tired all the time,” Ms. Hughes said. “My cycles are not regular anymore at all. When I do get one, it’s debilitating.” She is hoping a new job will provide insurance later this year.

Traditionally, most Americans with private health insurance got it through their jobs. But the job market has changed dramatically since 2010, particularly in the wake of the pandemic, with the rise of the gig economy.

Over 30 percent of people aged 18 to 29 said in recent surveys that they were working or have worked in short-term, part-time or irregular jobs.

The A.C.A. requires organizations with 50 or more employees to offer insurance to people working 30 hours per week. This has led to a growing number of contract employees who work up to, but not past, the hourly limit.

Many companies, who say they can’t afford the rising costs of traditional insurance, offer their employees only a modicum of help, perhaps around $200 per month toward buying a marketplace plan, or a bare-bones company plan.

Young people juggling part-time jobs and insurance options face bumpy, daunting transitions.

In Oklahoma, Daisy Creager, 29, has had three employers over the last three years. Insurance was important to her, not least because her former husband had Type 1 diabetes.

As she left the first of those jobs, her husband’s endocrinologist helped the couple stockpile less expensive insulin from Canada, since they would be uninsured.

After a few months, they bought a marketplace plan, but it was expensive and “didn’t cover a lot,” she said.

When she found a new job, she dropped that plan, only to discover that her new insurance coverage didn’t start until the end of her first month of employment. The couple would be uninsured for a few weeks.

A few days later, she came home to find her husband unconscious on the floor, in a diabetic coma. After hovering near death in an intensive care unit for four days, he woke up and began to recover.

“I think I’ve done everything right,” Ms. Creager said. “So why am I in a position where the health insurance available to me doesn’t cover what I need, or I can barely afford my premiums, or worse, at times I don’t even have it?”

Kathryn Russell, 27, developed excruciating back pain two months before her 26th birthday. After extensive testing, doctors determined that she needed a complex surgery, which her surgeon couldn’t schedule until after she would be off her family’s insurance plan.

Forget the pain and the fear of the operation, she said, it was insurance that kept her up at night. “There’s this impending terror of, ‘What am I going to do?” she recalled.

(One day before she turned 26, her father’s company agreed to keep her on his plan for six more months, if he paid higher premiums.)

The idea that the A.C.A. would offer a variety of good options for people turning 26 has not worked as well as the legislation’s authors had hoped. The so-called job lock tying insurance to employment has long plagued the United States work force.

Young adults need guidance in advance regarding their options, said Ms. Sanchez of Young Invincibles. None interviewed for this story, for example, knew that there were navigators to help them find insurance on the online marketplaces.

Experts agree that the marketplaces need stronger regulation.

In 2023, the federal government defined clearer standards for what plans in each tier of insurance should offer, such as better prescription drug benefits, defined co-pays for X-rays, or coverage for emergency room visits.

Certain types of basic care, such as primary care, should require just a small co-pay for at least a small number of initial visits. Each insurer must offer at least one plan that complies with these new standards at every tier of coverage — an “Easy Pricing” option or “standard plan.”

Most plans on the marketplaces don’t meet these criteria. Federal and state regulators had long planned to cull such “noncompliant” plans, but gradually, fearing that doing so too quickly would scare insurers away from participating.

But with the priorities of the new Trump administration now in focus, and a Republican majority in Congress, it’s far from clear what course Mr. Trump, who sought to repeal the A.C.A. outright in his first term, will take.

There are hints: Subsidies to help Americans buy insurance, adopted during the Biden administration, are set to expire at the end of 2025 if the Republican-led Congress doesn’t extend them.

If subsidies expire, premiums are likely to rise sharply for plans sold on the marketplaces, leaving insurance out of reach for many more young adults.