Williams, who will try to equal Margaret Court's record of 24 grand slam titles when she competes at the August 27-September 9 U.S. Open in NY, earned twice as much off the court as any other female athlete, according to Forbes.
Despite the vast amounts of money Serena earned in the past year, she is still made significantly less than the best paid male, Floyd Mayweather.
Serena Williams is the highest-paid female athlete of 2018, according to Forbes' annual list.
Dane Caroline Wozniacki, who captured her maiden grand slam title at this year's Australian Open, was second on the list with combined earnings of ($13 million) while reigning US Open champion Sloane Stephens ($11.2 million) was third.
The only non-tennis players in the top 10 are Indian badminton star P.V. Sindhu $8.5m (R122m) and racing's Danica Patrick $7.5m (R108m). Completing the top five are Spanish player Garbine Muguruza and Russia's Maria Sharapova who both earned more than $10 million over the past year.
Federer lost in the quarterfinals last year and this time in that round could face No. 6 seed Djokovic, the Wimbledon champion who beat him two weeks ago in a tuneup and is considered a tournament favorite after having to miss it last year because of injury.
The current WTA rankings are the usual criteria to decide seeding in the women's draw.
It was another instance of personal matters intruding on the tennis court in a way they never have before, with Williams opening up about her struggles with post-partum emotions since the birth of daughter Olympia last September, and wrestled with feelings of inadequacy that many new mothers experience.
Six-time U.S. Open champion Serena Williams could face sister Venus and then top seed Simona Halep in rounds three and four at Flushing Meadows this year.
Venus, who won five of her seven Grand Slam singles trophies in NY, is ranked and seeded 16th.