The Congressional Budget Office estimate comes as Trump has repeatedly threatened to halt the payments in his drive to dismember President Barack Obama's health care law.
The agency said 2018 premiums will grow "largely because of short-term market uncertainty — in particular, insurers' uncertainty about whether federal funding for certain subsidies that are currently available will continue to be provided."
It also attributed the projected increase to growing numbers of people living in regions where only one insurer sells policies, therefore facing less competition.
