Republican legislation that guts the Affordable Care Act would cause 18 million people to lose their insurance and would increase premiums of individual plans by about 20 to 25 percent, all within a year of being enacted, a report released today by the Congressional Budget Office estimates.

The legislation would destabilize the individual health insurance market, the report cautions, so the effects will “worsen over time.” After roughly two years, the number of uninsured would jump by 27 million and premiums would increase by about 50 percent. If nothing else changes, in ten years, the uninsured would increase by 32 million and premiums would be about double.

The CBO made the projections based on the most current insurance data and legislation introduced in 2015 by Tom Price (R-Ga.), President-elect Trump’s nominee for secretary of the Department of Health and Human Services. The legislation, H.R.3762, is designed to dismantle the ACA through budgetary reconciliation. The legislation passed both the House and Senate at the time but was vetoed by President Obama. The GOP has already begun legislative proceedings to once again pass a budgetary reconciliation that would demolish Obama’s signature healthcare law.

With the 2015 legislation, Price and his colleagues planned to undo the healthcare system in two phases.

First, immediately upon enactment, the bill would eliminate penalties for individuals without insurance (the individual mandate) and for employers who don’t offer insurance meeting ACA-defined standards (the employer mandate). The CBO estimates that in the first full insurance plan year after that, 10 million people will lose the insurance they got in the individual market, 5 million fewer people will be covered by Medicaid, and 3 million will lose employer-based coverage.

Many insurance companies would leave the individual insurance market and about 10 percent of Americans will have no options for individual insurance plans.

Mostly healthy and young people will exit the insurance pool at this point, leaving a higher proportion of the less healthy and older, who tend to use healthcare more and are thus more expensive to insure. Thus, premiums will increase by about 20 to 25 percent.

In the second phase, roughly two years after enactment, the plan will eliminate the ACA’s Medicaid expansion and subsidies. This will increase the number of uninsured by 27 million and premiums would be around 50 percent higher. About half of the country will not have access to an individual insurance plan.

If no replacement plans are enacted, things will continue to erode by 2026, and about half of the country’s population wouldn’t have access to an individual plan.

Republicans have vowed to not just repeal the ACA but to replace it with other healthcare legislation. However, the party has yet to come to a consensus on a detailed replacement plan.