WASHINGTON — Fewer people than expected are purchasing health insurance under President Barack Obama’s health care law, a report confirmed Monday.

The Congressional Budget Office study said 13 million people are likely to purchase policies through the Affordable Care Act this year, down about 8 million from estimates the agency made early last year. That’s based on updated enrollment figures through last month.

The Department of Health and Human Services had already flagged the lowered expectations last fall, predicting just 10 million customers.

The federal and state markets offer subsidized private insurance to people who don’t have access to job-based coverage. Fewer unsubsidized customers are buying through the exchanges, the budget office said.

The CBO’s latest report reduces the agency’s expectations for President Barack Obama’s health care law, bringing it closer to more modest goals that the administration has set.

At issue is enrollment in the law’s health insurance markets, or exchanges, which offer subsidized private coverage.

Previously, the budget office had projected a monthly average of 21 million enrolled in 2016, with 15 million of those customers receiving taxpayer-financed subsidies to help pay their premiums.

Monday’s estimate is for a monthly enrollment of 13 million, with 11 million of those receiving subsidies.

The new estimates reflect a growing consensus that it’s going to take longer for the online insurance markets to achieve their full potential.