However, the more disturbing news, she said, is how hard it is for women to get back on track after that time off. Although 93 percent of women want to go back to work, only 74 percent succeed in getting back in. "And those who get back in pay a big penalty," Hewlett said.
According to the task force's report, the results of which appeared this month in the Harvard Business Review, 37 percent of the women surveyed reported they took voluntary time off work for any reason. Of the women who had children, 43 percent took time off. Meanwhile, 24 percent of the men reported they took voluntary time off from their careers.
Women left work for a relatively short period of time, 2.2 years on average, the survey showed. However, the career interruption took a toll. They lost an average of 18 percent of their earning power when they took time off, according to the study. In business sectors, women's earning power dropped 28 percent when they took leave. And in all sectors, if they took off for three years or more, they earned 37 percent less than their peers when they returned.
That drop partly reflects women who came back part time or took jobs with less responsibility. But it also may mean women are jumping off the career track just as men are making career leaps, Hewlett said.
Women who opt out, at least temporarily, are not leaving because work is hard. In fact, the more demanding the work, the more women stayed, said Carolyn Buck Luce, global managing partner for Ernst & Young's health sciences industry practice in New York.
Only 6 percent of the women said they stopped working because the work was too demanding, according to the study.
A majority (58 percent) of women in the study describe their careers as "non-linear," meaning they don't follow the standard career path that many successful men do.
If companies expect to keep a talented workforce, and keep that workforce motivated, they must also accommodate life. So if a woman comes back to work and doesn't choose to put in 80 hours a week, that doesn't mean she's not motivated or does not want to be challenged, Luce said. She pointed out that 10 percent of Ernst and Young's female partners are on some sort of flexible schedule.
The study, Luce and Hewlett said, put numbers to what many women anecdotally knew to be true. And the group hopes to start to change how corporations treat women who try to return to work after leave.
"We want to be able to tie all this together so that we really have a better understanding of how corporations globally can have lifelong relationships with female employees," Luce said.
Join Amy Joyce from 11 a.m. to noon Tuesday at washingtonpost.comto discuss your life at work. Do you have a situation at work that would make a good column? E-mail email@example.com.