At the US Open, like all tennis majors, women earn the same amount as men — but this wasn’t always the case. The Guardian charted female champions’ prize money as a percentage of men’s for each grand slam since the beginning of the Open era. Explore the road to pay equality below

Battle of the sexes: charting how women in tennis achieved equal pay

Battle of the sexes: charting how women in tennis achieved equal pay

When the winners of the 2015 US Open are crowned this weekend, the men’s and women’s champions will each walk away with $3.3m — a rare example of pay equality in sports.

By contrast, earlier this summer the USA team who won the women’s World Cup earned a fraction of the sum Germany earned for winning the men’s World Cup in 2014 — $2m compared to $35m. Many other sports, including professional basketball and golf, have similarly striking pay disparities.

In all four tennis majors (and many standalone tournaments), pay is equal. But this wasn’t always the case.

To visualize the road to equality, the Guardian requested historical prize money for the singles champions from each major tournament and calculated what percentage of the men’s award women earned each year.

The US Open was the first major to offer equal pay back in 1973, after women’s champion Billie Jean King threatened to organize a boycott of the tournament. Just one year prior, King earned $10,000 for first prize — 40% of Ilie Năstase’s $25,000 award.

It took 28 years until another grand slam consistently awarded equal prize money.

The Australian Open offered female and male champions the same size prize in the mid 80s and early 90s — women were even paid slightly more than men in 1987 and 1988 — according to Tennis Australia’s records. But pay equality lapsed over several years. Finally, in 2001, the Australian Open became only the second tournament to commit to parity.

After years of almost-but-not-quite-equal pay, the French Open, gave women’s and men’s champions equal money in 2006. Wimbledon held out for another year.

With backing from the Women’s Tennis Association, another American tennis star, Venus Williams, played a key role in the final push for parity.

“Why does Wimbledon choose to place a lesser value on my championship trophy than that of the 2005 men’s winner Roger Federer?” she wrote in a 2006 article.

Responding to critics who argue that women deserve to be paid less because they play less (best-of-three sets versus men’s best-of-five), she dryly noted that, “for the record, the ladies’ final at Wimbledon in 2005 lasted 45 minutes longer than the men’s. No extra charge.”

When Williams and Federer returned to the champions’ podium in 2007, they were awarded equal pay.

This year’s US Open saw another historic first thanks to Venus’s sister, Serena: the women’s final sold out before the men’s.