In any given month this year, about 13 million people on average are now expected to be enrolled in a health plan purchased on a marketplace created by the law, often called Obamacare.

That is down from 21 million people previously estimated by the budget office, whose projections about the impact of legislation are closely watched by both parties in Washington.

The lower enrollment number brings the budget office closer in line with the Obama administration, which scaled back its own enrollment targets for 2016, citing the difficulty of reaching new consumers who have not so far taken advantage of the marketplaces.