What you need to know about Equal Pay Day

— -- Today is "Equal Pay Day," or the day that signifies how far into the year a woman must work to earn what her male colleagues were paid the previous year.

Here's what you need to know:

When did Equal Pay Day start?

The day was started by National Committee on Pay Equity in 1996 to bring awareness to the gap between men and women's wages. The day is observed in other countries as well, but not necessarily on the same day as the U.S. due to differing income disparities.

In previous years, grassroots organizations, women's businesses, professional organizations, labor groups and more have rallied together on Equal Pay Day to find solutions for wage inequity.

How is Equal Pay Day chosen?

While the day is symbolic in nature, the National Committee on Pay Equity chooses a Tuesday in April because Tuesdays signify how far into the next work week a woman must work to earn a man’s wages from the previous week. The date fluctuates yearly to avoid religious holidays and significant events. Typically, Equal Pay Day is the second week in April, but this year it was likely moved earlier to avoid Passover next week.

How big is the gap?

In 2015, full-time/year-round female workers earned 79.6 percent of what their male counterparts made, according to the Institute for Women’s Policy Research (IWPR). The gap is greater for black and Hispanic women.

There has not been a statistically significant annual increase in women’s wages since 2007, and if the pace of change in annual earnings remains the same, it will take 45 years for women to earn as much as men, the IWPR states.

What's being said about it

President Donald Trump's daughter Ivanka Trump, who recently took an unpaid position in her father’s administration, posted about the day on Instagram.

"Today, on #EqualPayDay, we are reminded that women deserve equal pay for equal work," she wrote.

She added: "Closing the gender pay gap is critical to the economic empowerment of American women, and it is the responsibility of all Americans to come together in pursuit of equal pay. I am proud to work towards this goal alongside my father and in support of the administration’s commitment to women and families."

Meanwhile, Chelsea Clinton tweeted “Yes. Yes. Yes. Closing the #wagegap is crucial to a strong economy. #EqualPayDay"

Senate Minority Leader Chuck Schumer, D-New York, wrote on Twitter: "The #PayGap doesn't just impact women's take home pay—think about retirement, pensions, healthcare coverage & everything else!"

House Minority Leader Nancy Pelosi, D-California, posted a series of tweets, including: "The Pay Gap is an affront to women's contributions to our communities. #EqualPayDay"