Bill Gates last week ceded his title as Microsoft's largest individual shareholder to former CEO Steve Ballmer.
It was the first time in Microsoft's nearly 40 years that Gates, 58, was not the company's top shareholder.
Gates, who co-founded Microsoft in 1975, served as CEO until 2000 and only stepped down as chairman in February, sold a total of 7.85 million shares in transactions on April 29 and 30, according to documents filed with the U.S. Securities and Exchange Commission (SEC).
Geekwire first reported on the investment milestone.
The sales generated $317.5 million before taxes, and reduced Gates' holdings to approximately 330.1 million shares. Ballmer currently owns about 333.3 million shares, a number that has stayed stable for several years.
Gates, on the other hand, has been selling an average of 80 million shares annually for the last decade in a long-standing plan to fund the Bill & Melinda Gates Foundation. Gates has pledged to give away the bulk of his wealth.
If he continues his divestiture, Gates will sell an additional 12.15 million shares between now and June 30, the end of the current quarter, to make his usual 20 million shares per quarter mark. Gates will have exhausted his holdings by September 2018 unless he stops or slows his selling.
Gates' remaining shares were worth approximately $13.1 billion at Friday's closing price. His total wealth, however, has been pegged significantly higher: Forbes recently estimated Gates' net worth at $77.2 billion, making him the wealthiest person on the planet.
The abdication of his shareholder crown was the second major change for Gates in his relationship with Microsoft this year. On Feb. 4, the day Microsoft announced Satya Nadella as its new CEO, Gates vacated his role as chairman of the board to become a hands-on advisor to Nadella on technology and product selection decisions.
Gates remains a director on the board.
Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at @gkeizer, on Google+ or subscribe to Gregg's RSS feed . His email address is email@example.com.