CNBC reports the donation marked the halfway point for Buffett, 90, who initially pledged to give away all of his Berkshire shares through annual gifts to the Gates' foundation, Susan Thompson Buffett Foundation, Sherwood Foundation, Howard G. Buffett Foundation and NoVo Foundation in 2006. Buffett owned 474,998 Berkshire A shares in 2006 and said he currently owns 238,624 shares, which is estimated to be valued at about $100 billion. “Today is a milestone for me,” Buffett said in a statement obtained by CNBC. “In 2006, I pledged to distribute all of my Berkshire Hathaway shares — more than 99% of my net worth — to philanthropy. With today’s $4.1 billion distribution, I’m halfway there.”