Can someone spend more than 20% on ma’aser or tzedakah?
The Gemara writes that a person should not spend more than 20% for charity contribution. According to some authorities (Birkei Yosef, Yoreh De’ah 249; Minchas Pittim; Iggros Moshe, Yoreh De’ah 143), this halachah applies even to somebody who is very wealthy. Even the extremely rich must remind themselves that someday, they may require the assistance of others. However, it is permitted to donate to other worthy causes that are not officially considered to be tzedakah.
Yet, other poskim, including the Yaavatz (Yoreh De’ah 249), Chochmas Adam 144:6, and others (see Rishon Le-Zion of the Or Ha-Chaim; Chafetz Chaim, Ahavas Chesed chap. 20; Rav Shlomo Zalman Auerbach, quoted in Be’Orach Tzedakah p. 324) rule that it is permitted for a very wealthy person to donate more than 20%, and this is the common custom.
Therefore, a person of ordinary wealth may not donate more than 20%, but for somebody who is extremely wealthy it is permitted. This is also the ruling given by Shevet Halevi (2:121) and Minchas Yitzchak (5:34:2).