WASHINGTON — The nonpartisan Congressional Budget Office said on Tuesday that repealing major provisions of the Affordable Care Act, while leaving other parts in place, would cost 18 million people their insurance in the first year and could increase the number of uninsured Americans by 32 million in 10 years, while causing individual insurance premiums to double over that time.
The budget office analyzed the probable effects of a Republican repeal bill like the one approved in Congress but vetoed early last year by President Obama.
The C.B.O. report, released after a weekend of protests against repeal, will only add to the headaches that President-elect Donald J. Trump and congressional Republicans face in their rush to gut President Obama’s signature domestic achievement and try to replace it with a health insurance law more to their liking.
The bill that the budget office analyzed would have eliminated tax penalties for people who go without insurance. It would also have eliminated spending for the expansion of Medicaid and subsidies that help lower-income people buy private insurance. But the bill preserved requirements for insurers to provide coverage, at standard rates, to any applicant, regardless of pre-existing medical conditions.
“Eliminating the mandate penalties and the subsidies while retaining the market reforms would destabilize the nongroup market, and the effect would worsen over time,” the budget office said.
The report is likely to slow efforts to dismantle the health care law. Mr. Trump and Republican lawmakers say they intend to replace the law, but they have not agreed on a replacement plan.
The budget office said the estimated increase of 32 million people without coverage in 2026 resulted from three changes: about 23 million fewer people would have coverage in the individual insurance market, roughly 19 million fewer people would have Medicaid coverage, and there would be an increase in the number of people with employment-based insurance that would partially offset those losses.