WASHINGTON – More than a third of young American adults live with his or her parents, a 40-year high, a study released Thursday by the Pew Research Institute suggests.

In 2012, 36 percent of Americans aged 18 to 31 – or 21.6 million— lived with their parents, compared with 18.5 million in 2007, the year the Great Recession began.

At least one in three of the stay-at-homes were students.

Those aged 18 to 24 were most likely to remain in the proverbial family nest, compared with 16 percent of the 25- to 31-year-olds.

Pew’s research team also found that males were more likely than females to share a roof with mom and dad— 40 percent versus 32 percent.

Pew attributed the slow but steady rise to unemployment, which hits young people especially hard, as well as higher university admissions and fewer marriages.