Today is Equal Pay Day, which was invented by an activist group two decades ago to draw attention to the wage divide between men and women.
The day comes in April, marking how many extra months women would have to work into the new year to make what men made the year before.
The divide in pay has narrowed since 1996, but women in the U.S. still make about 80 cents for every dollar a man earns, according to census data.
Here are some basic facts about that persistent gap:
In California, the difference is $7,227 a year
A woman who works full time in California makes a median income of $43,335, compared with a median of $50,562 for a man, according to an analysis of Census Bureau data conducted by the National Partnership for Women and Families, an advocacy group.
That makes for a difference of a little more than $7,200 a year, or the average cost of more than five months of rent in the state.
California's Latina women are further behind — they earn just 43 cents on the dollar, compared with white men. Black women earn 63 cents, and Asian women earn 72 cents.
In total, the analysis found, women in California would earn $78.6 billion more per year if their mean pay were same as men's.
Women are in lower-paying jobs
Although the pay gap was present across industries and within occupations, much of it can be attributed to differences in occupation and industry: Women tend to go into fields where salaries are lower and perform jobs that pay less.
That's a key takeaway from a 2016 study by two Cornell economists, Francine Blau and Lawrence Kahn, published by the National Bureau of Economic Research. They found that 51% of the difference in the compensation of women and men is related to the fact that female workers are more concentrated in underpaid sectors, such as nursing and education, and in lower-level roles.
Women have managed to overtake men in education and almost completely catch up in experience over the past three decades. But the divide in the types of careers women and men gravitate toward persists, and seems to hold back women's pay.
Women ask for less money
When hunting for a new job, women ask for lower salaries than men, and they leave the table with less money, according to a study published last year by Hired, a website that connects employers to job seekers.
The website studied data from 100,000 salary offers for tech, marketing and sales jobs, and it found that nationally women asked for an average of $14,000 less in compensation than men overall. Employers offered women about 3% less than what they offered men to fill the same position, with the same job title, the analysis showed.
In Los Angeles, women asked for $10,000 less than men, and took home $8,000 less. In San Francisco, they asked for $12,000 less and received about $9,000 less.
Those expectations mattered: Women who asked for bigger salaries than men ended up getting them.
Women just entering the job market, with less than two years of experience, expected to get paid a little bit more than men, the Hired study found. More experienced women expected to get paid less. The junior women left negotiations with salaries that were 7% higher than those of junior men.
Women make up nearly half the labor force
Women accounted for 46.8% of the U.S. labor force in 2016, according to the Bureau of Labor Statistics. That's a lot of progress since 1950, when women made up 29.6%, according to historical data analyzed by the Pew Research Center.
But the female share of the workforce appears to have plateaued in recent years. The bureau projects it will peak at 47.1% in 2025 and then taper off, meaning women would remain a minority in the workforce.
The decline in labor force participation can have negative effects on the nation's productivity and standard of living, according to Pew.
Discrimination is probably still happening
The Cornell study found that a chunk of the pay differential could not be explained by measurable qualities of American workplaces. The authors say that one hard-to-quantify factor at play could be discrimination.
Indeed, research has shown that many women with the same credentials who work in the same exact jobs as men earn less. A 2015 Bloomberg analysis of more than 12,000 MBAs found that, eight years out of business school, women earned 20% less than the men they graduated with.
The divide persisted within industries, job functions and for people who got their degree from the same business school.
Census data also show that women are paid less than men within the industries where most Americans work, including healthcare, education and manufacturing, and within specific jobs, like sales, management, production and administrative functions.
What's more, it seems that women cannot always choose to make more than men by shifting into a higher paying field. A comprehensive study of census data from 1950 through 2000 found that as women began working in occupations that once were dominated by men — as biologists or designers, for example — the compensation in those jobs declined.