Here's a Vox post on the donations to charity by the most wealthy Amercans. As Dylan Matthews notes, there are a number of qualifications and cautions in interpreting the figures. For my purposes,only three billionaires, Bloomberg, Gates, and Buffett gave more than 1 percent of their wealth in the last year.
I may have discussed this before in connection with Warren's proposed wealth tax. Anyhow, retirees are told they can withdraw 4 percent of their savings and likely not exhaust them before dying. I think maybe that's a reasonable target: once a person reaches retirement age, between taxes and charity the total should be about 4 percent of wealth.