Things are improving so slowly for women in corporate America that we arent going to achieve gender equality at the top for another 100 years, according to a report released Wednesday.

It's not for the reasons you might think -- i.e., it's not a mommy issue. Both women and men reported feeling strained by the competing pulls of work and family, according to the survey of nearly 30,000 workers at 118 North American companies. The survey was conducted by McKinsey & Company and LeanIn.org, a nonprofit focused on women's advancement founded by Sheryl Sandberg, chief operating officer at Facebook .

The big, ugly, hard-to-fix issue, the study suggests, is gender bias. That contradicts a lot of the conventional wisdom about why women dont make it to the so-called C-suite -- the highest levels of a company where you find the jobs with chief in the title, like chief executive and chief finance officer. Only 17 percent of those lofty positions are held by women, according to the McKinsey/LeanIn survey. There are only 24 female CEOs on Fortunes list of the 500 biggest companies in the U.S. That's an improvement from 1998, when there was just one woman on the list , but it still means that men hold the chief executive spot at over 95 percent of those businesses.