$40.3 bln is the endowment balance of the Bill & Melinda Gates Foundation, the world’s largest private charitable foundation, according to Forbes A promise is one thing. plunking down actual cash is another. Forbes’s annual list of America’s top philanthropists, compiled in partnership with Shook Research, makes that important distinction: It tallies who gave away the largest amount last year in dollar terms, not who merely pledged the most. The top 20 are below for the full list, see forbes.com/top-givers .