The Chronicle of Philanthropy calculated the giving since 2000 of the 10 richest people in America, and calculated their charity as a share of their total wealth.
Buffett topped the list, giving away more than $46 billion since 2000. That worked out to 71 percent of his $65.5 billion fortune.
The billionaires' wealth levels were from Forbes as of the end of 2016. Many of those fortunes are now higher. The Chronicle's calculations were based on the Philanthropy 50 reports, data from the IRS and information supplied by some of the donors.
Gates has given away $18 billion, or 22 percent of his $81 billion fortune, to charity since 2000. Yet he and Melinda Gates have given away more than twice that since they created their foundation in 1994. And last month, he donated another $4.6 billion in Microsoft stock.
Michael Bloomberg ranked third, with 10 percent of his $45 billion fortune going to charity, That too is understated, since it doesn't count his giving before 2000 or possible anonymous gifts.