The 29 percent includes women who are married, single, disabled, enrolled in school or unable to find work.
The largest share of at-home mothers — roughly two-thirds of 10.4 million — had working husbands. A growing share — 6 percent in 2012, up from 1 percent in 2000 — said they could not find a job, according to Pew, which relied on U.S. Census and other government data.
No matter what their marital status, mothers at home are younger and less educated than working counterparts, the report said. Most married moms said they were home specifically to care for the kids, while single mothers were more likely to say they couldn't find a job, were ill or disabled or were in school.
Among all at-home mothers in 2012, 51 percent had at least one child 5 or younger, compared with 41 percent of working mothers.
The researchers said one of the most striking demographic differences between at-home mothers and working mothers is their economic well-being, with about 34 percent of at-home mothers living in poverty, compared with 12 percent of working mothers.
Relatively few married at-home mothers with working husbands qualify as "affluent," at nearly 370,000 with at least a master's degree and a median family income of over $75,000 a year in 2012. That number amounts to 5 percent of married at-home mothers with working husbands.
The "elite" marrieds stand out from other at-home mothers as disproportionately white or Asian. About 69 percent are white and 19 percent are Asian. Only 7 percent are Hispanic and 3 percent are black.
Mothers more likely to stay home are among demographic groups on the rise in the U.S. For example, 40 percent of immigrant mothers were at home with their children, compared with about a quarter of mothers born in this country.
Among at-home mothers living in poverty in 2012, 36 percent were immigrants, the report said.
While clearly attitudes over the decades toward working mothers have grown warmer, "most Americans continue to believe that it's best for children to have a parent at home," said D'Vera Cohn, a senior writer at Pew who worked on the report.
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