Today is Equal Pay Day, marking the 99 extra days women have to work this year to equal the pay men were paid last year.

Data from the National Committee on Pay Equity show the wage gap between women and men narrowed slightly last year. Women are now paid 80 cents for every dollar paid to men.

According to Toni Van Pelt, president of the National Organization for Women, the research shows that progress toward equal pay has moved at a snail’s pace since the Equal Pay Act was signed into law by President John F. Kennedy in 1963.

“When we first started talking about this, the average full-time working woman was earning 59 cents,” Van Pelt said, “so in 55 years, it’s only closed by 18 cents.”

She added the pay gap is even greater for women of color, with African-American women earning an average of 66 cents, and Latinas just 60 cents, to every dollar paid to men.

Van Pelt pointed out the huge impact that this pay gap can have over the course of a lifetime, as hourly pay itself is just part of total lifetime earnings.

“Pension benefits, our vacation time, our care-giving time – all of these things can be based on how much a woman is paid,” she observed. “And so, it’s really important that she has equal pay.”

On average, a woman’s lifetime earnings are $530,000 less than a man’s. And Van Pelt noted that lower pay for women affects more than their purchasing power.

“If women are kept in a state of constant economic insecurity, they are more liable to feel that they must put up with sexual harassment and sexual assault in the workplace,” she said.

A study by the Institute for Women’s Policy Research found that, at the current pace, white women will achieve pay equity with white men in about 40 years. But for African-American women, it will take 100 years, and for Latinas, more than two centuries.