You've probably heard the stat about how for every dollar men make, women make just 80 cents — but there's a lot about the pay gap that might still surprise you.

April 4 marks Equal Pay Day, which represents the number of days this year women have essentially worked "for free" as the result of the wage gap. While the day is an excellent moment to raise awareness about society's inequalities, fighting for fair pay and equal rights is something you can do 365 days a year.

Students at Barnard College attend the school's 2016 commencement ceremony. Photo by Timothy A. Clary/AFP/Getty Images.

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If you're in the mood to be surprised, angered, encouraged, or just plain informed, check out these 23 interesting facts about equal pay.

1. Even Batgirl had to fight for equal pay.

2. On average, it takes women 459 days to make as much as men do in a single year. (This is kind of the whole point of Equal Pay Day.)

The British-based National Women's Liberation Movement protests in London in 1971. Photo by Daily Express/Hulton Archive/Getty Images.

3. Even when women "lean in" and negotiate harder, they're less likely to get raises than men.

4. Women lose out on an estimated $419,000 over the course of a lifetime as the result of the pay gap. What?!

A Miami woman protests on International Women's Day. Photo by Joe Raedle/Getty Images.

5. What does a year’s worth of lost wages (an average of $10,470) add up to? For starters: 15 months of child care, 78 weeks of food for a family, 11 months of rent, nearly nine years of birth control, or 1.2 years’ tuition at a four-year public university.

6. Millennial women across the political spectrum say they’re more likely to support politicians who fight for equal pay, including 70% of Republicans, 83% of Independents, and 88% of Democrats.

7. There's some good news: The pay gap is closing. There’s also a bit of bad news: None of us will be alive to see it. One estimate suggests that we’ll be waiting until 2152 for paycheck equality. Ooof!

A cheeky lemonade stand highlights the pay gap. Photo by Molly Riley/AFP/Getty Images.

8. Yes, it’s illegal to pay women less than men for the same work (thanks, Equal Pay Act of 1963!) Unfortunately, it still happens. There's not exactly a whole lot of transparency when it comes to wages, and enforcing the law means an employee has to learn they're being discriminated against and then take their employer to court. Without additional steps to encourage transparency and reduce the possibility of retribution, the law doesn't quite cut it.

9. The first bill President Obama signed into law was the Lilly Ledbetter Fair Pay Act, which got rid of the 180-day statute of limitations on wage discrimination claims. In other words, it made it so that if you found out your employer had been discriminating against you for years, you’d be due damages on the whole time, not just the last six months.

Lilly Ledbetter watches as President Obama signs the law bearing her name. Photo by AP Photo/Susan Walsh.

10. Fun fact: If we eliminated the pay gap, poverty among working women would decline by more than half in 28 states!

11. From a “What can I get on my member of Congress’ case about?” point of view, the Paycheck Fairness Act is a good place to start. The bill would help make wages more transparent, would require your bosses to prove that any differences in pay are actually related to qualifications, and would block companies from retaliating against employees who raise concerns about discrimination. There's a whole list of things you can chat with your Congressperson about when it comes to pay equality.

President Obama signs an executive order banning federal contractors from retaliating against employees who raise concerns about pay discrimination in 2014. In March 2017, President Trump rescinded the order. Photo by Mark Wilson/Getty Images.

12. The pay gap isn’t a myth. It’s math. Even when you control for things like age, experience, race, location, and education, it’s still just as real as ever.

13. Not all states are equally unequal! For example, the pay gap in North Carolina (where women make 86% of what men do) is much smaller than in Wyoming (where women make just 64% of what men do).

Jensen Walcott (right) speaks at the 2016 Democratic National Convention. Walcott was fired from her job for asking for equal pay. Photo by Saul Loeb/AFP/Getty Images.

14. The most surefire way to score a box office hit in 2016 was to cast Scarlett Johansson, that year’s top-grossing actor (that is, her movies made more money than any other actor's). Even so, a quick look at the five highest-paid actors of the year is just a bunch of dudes. Really?

Scarlett Johansson. Photo by Jason Merritt/Getty Images.

15. In 2016, the women of Iceland protested the wage gap by going on strike. In response, lawmakers recently unveiled a five-year plan to get the country to paycheck equality.

16. Women in Australia are trying a similar tactic: walking off the job at 3:20 p.m., the time that women in the country basically start working for free because of the wage gap.

Child care workers march for higher wages on March 8, 2017, in Melbourne, Australia. Photo by Scott Barbour/Getty Images.

17. Despite now being America’s most educated group, black women are hit especially hard by the wage gap, making on average nearly $20,000 a year less than white men. What even?

18. Actress Emmy Rossum took a bold stand for pay equality, pushing to get paid the same as William H. Macy, her male counterpart on the set of Showtime’s “Shameless.” And guess what? It worked. She even got paid back wages for earlier seasons.

Emmy Rossum. Photo by Monica Schipper/Getty Images for Variety.

19. So did “Star Wars” actress Felicity Jones.

20. As did “X-Files” actress Gillian Anderson.

"X-Files" stars David Duchovny and Gillian Anderson. Photo by Frederick M. Brown/Getty Images.

21. One way companies can show they're taking the fight for wage equality seriously is by getting EDGE (Economic Dividends for Gender Equality) certified. If you're in a position to push the company you work for to get involved, give it a shot!

Image via iStock.

22. Another thing you can do is support companies that met President Obama's 2016 Equal Pay Pledge and encourage other companies to make similar public statements.

23. And if you're looking to hone your own negotiating skills, there's even a Facebook chat bot that'll help you navigate your way to a fair wage.

No matter your gender, equal pay is something worth fighting for — and yes, there are things you can do to help out.

The above list has a few suggestions, but you can learn about other ways to help out over at the American Association of University Women's website. Every week, they post a new action you can take to help build a better, more fair world for us, our children, grandchildren, and beyond.

A Fort Lauderdale, Florida, woman joins a March 14, 2017, protest calling for equal pay. Photo by Joe Raedle/Getty Images.

We all have an important role to play in fighting discrimination. Whether you're a man, a woman, a business owner, a legislator, or just someone who believes in equality, there are concrete steps people can take.