Celia Monreal worries every day about the cartilage loss in her husband’s knees. Not just because it’s hard for her to see him in pain but also because she knows soon their health care costs could skyrocket.

Monreal, 47, and her husband, Jorge, 57, rely on the Affordable Care Act marketplace for health coverage. If Congress doesn’t extend certain ACA tax credits set to expire at the end of the year, their fully subsidized plan will increase in cost, putting it out of reach. Without insurance, they won’t be able to afford his expected knee replacement surgeries, much less the treatment they need for other issues, like her chronic high blood pressure and his high cholesterol.

“It worries me sometimes, because if you’re not healthy, then you’re not here for your kids,” Monreal said. “It’s a difficult decision, because, OK, do I spend $500 on a doctor’s visit or do I buy groceries?”

Those are the types of choices facing the millions of Americans whose state or federal marketplace health insurance plans will be up for renewal in November. The enhanced premium tax credits that have made coverage more affordable for low- and middle-income enrollees for the last four years will expire this year if Congress doesn’t extend them. On average, that will more than double what subsidized enrollees currently pay for premiums next year, according to an analysis by health care research nonprofit KFF.

The tax credits are at the heart of the federal government shutdown, in its third week with no end in sight. Democrats have demanded the subsidies be extended as part of any funding deal they sign, while Republicans say they’ll only negotiate on the issue once the government is funded.

With Congress deadlocked and the open enrollment period for ACA plans approaching on Nov. 1 in most states, Americans like Monreal are left to navigate the unknown.

No extension will mean higher premiums for millions

More than 24 million people have ACA health insurance, a group including farmers, ranchers, small business owners and other self-employed people who don’t have other health insurance options through their work.

The enhanced premium tax credits set to expire this year have made costs far more manageable for many of them, allowing some lower-income enrollees to get health care with no premiums and higher earners to pay no more than 8.5% of their income.

If the tax credits expire, annual out-of-pocket premiums are estimated to increase by 114% — an average of $1,016 — next year, according to the KFF analysis.

While some premium tax credits will remain, the level of support will decrease for most enrollees. Anyone earning more than 400% of the poverty level — or around $63,000 per year for a single person — won’t be eligible for the remaining tax credits.

As a result, especially hard-hit groups will include a small number of higher earners who’ll have to pay a lot more without the extra subsidies and a large number of lower earners who’ll have to pay a small amount more, said Cynthia Cox, a vice president and director of the ACA program at KFF.

With higher premiums, some people will drop out of health insurance altogether, Cox said. When many younger, healthier people inevitably forgo coverage, insurance companies will increase costs for members of the covered population to account for them being older and sicker.

The change may also strain hospitals, since more uninsured people will need emergency care they can’t afford. That could lead to hospital closures or cost increases.

“If you have less subsidies for people getting health insurance, you’re going to have less health coverage and less health care,” said Jason Levitis, a senior fellow in the health policy division at the Urban Institute. “People are going to be sicker and die more.”