Today is Equal Pay Day, chosen as April 8, the symbolic date when women’s wages catch up to men’s from the previous year. Today is also the day that President Obama, lacking support from Congress on equal pay measures, signed an executive order barring federal contractors from retaliating against employees who discuss their pay with one another. He also directed the Labor Department to adopt rules requiring federal contractors to provide compensation data based on sex and race.

“Pay secrecy fosters discrimination, and we should not tolerate it, not in federal contracting or anywhere else,” Obama said at the signing. He was joined at the White House by Lilly Ledbetter, whose name appears on a pay discrimination law Obama signed in 2009.

Some dismiss the gender pay gap as due to women’s occupational and lifestyle choices, but data analysis by labor economists Francine Blau and Lawrence Kahn concluded that over 40 percent of the pay gap cannot be explained by such differences. To understand why this really outrages women and enlightened men, have a look at the depth of the problem here.

THE PROBLEM

There are a number of ways to look at the pay disparities between men and women. This chart from The American Association of University Women (AAUW) shows women’s median annual earnings as a percentage of men’s over the past 40 years. The pay gap has steadily narrowed over time, but it’s progress has stalled in recent years.

The Pay Gap Over Time

Women’s Median Annual Earnings as a Percentage of Men’s Median Annual Earnings

for Full-time, Year-Round Workers, 1972–2012

Pew Research looked at the pay gap by examining hourly earnings, estimated as usual weekly earnings divided by usual hours worked, because it “irons out differences in earnings due to differences in hours worked.” As such, Pew’s calculations take into account that women are twice as likely to work part-time as men, 26 percent versus 13 percent. They found that for every dollar a man earns, a woman earns $0.84.

IN YOUR STATE

The AAUW used the most recent statistics from the US Census Bureau to show the gender pay gap in states, as well as congressional districts. In Maryland, where the gender pay gap is second-smallest only to that of Washington, DC, women were paid 85 percent of what men were paid in 2012. Wyoming is on the opposite side of the spectrum with the most pay inequality, with women paid just 64 percent of what men were paid.

IT ADDS UP!

Comparing earnings between men and women, the Center for American Progress created this infographic below to show how the pay gap added up over time, using 2010 data. That year, the median full-time working man had earnings of $47,715 in earnings, compared to $36,931 for women. That pay difference of $10,784 adds up to $431,360 over 40 years! Here’s what women, and their families, are missing out on.

MILLENNIALS ARE STARTING TO CLOSE THE GAP

A survey by Pew Research found that young women are closing the wage gap with men: In 2012, among workers ages 25 to 34, women’s hourly earnings were 93 percent of those of men. Still, the survey found that these young women believe the fight is far from over. Seventy-five percent said America needs to do more to achieve gender equality in the workplace, compared with 57 percent of millennial men.