The Congressional Budget Office and the Joint Committee on Taxation predict there will be 3 million fewer Americans with health insurance in 2019 when the ACA's individual mandate is eliminated.
CBO and JCT also said rising premiums in the individual market will contribute to an increase in uninsured Americans next year.
"The nongroup health insurance market is stable in most areas of the country over the next decade in CBO and JCT's projections — but that stability may be fragile in some places," the agencies said. "In 2018, insurers are offering coverage in all areas, but about one-quarter of enrollees have access to only one insurer's plans."
During the next 10 years, both the number of people with insurance and the number of people without insurance are expected to rise. The share of Americans under age 65 without health insurance will reach 13 percent by 2028, according to CBO and JCT.
In addition, the agencies expect premiums for benchmark individual plans to climb 15 percent for 2019.
The ACA's individual mandate was repealed under new federal tax regulation.