Halacha Corner: How Much Charity Should One Give?
A person who gives charity to the poor, especially one who supports Torah scholars, receives great reward. Through charity, one can avert harsh decrees, as charity saves from death.

Regarding the measure of charity, our Sages, Rambam, the Tur, and Maran in Shulchan Aruch wrote: "If one can afford it, they should give according to the needs of the poor." This means that if one is very wealthy and can provide for all the needs of the poor in their city and so forth, they should give them whatever they lack. "If one cannot afford that much, they should give up to a fifth of their possessions as the preferred way" - meaning, they should give up to a fifth of their wealth to charity, which is the ideal fulfillment of the mitzvah. "If a person gives one-tenth of what they have, this is considered an average measure," meaning, although it's not as praiseworthy as giving a fifth, it's still a moderate measure to give a tenth of one's possessions, as many righteous people practice, giving "ma'aser kesafim" (tithing money), allocating a tenth of their profits to charity. Less than this, meaning someone who doesn't even give a tenth of their money, is considered stingy, as they are reluctant to share even a small portion of their wealth with others.
This measure of giving a fifth, which is the best of all, is derived from the verses, as it says: "And of all that You give me, I will surely give a tenth to You." The double expression "give a tenth" implies giving a tenth twice, and two tenths equal a fifth. Rabbeinu Tur wrote that it is tested and proven that because of the charity one gives, they will not lack anything; rather, it will increase their wealth and honor, as it is said: "Since they began to bring the contributions into the house of Hashem, we have eaten and been satisfied and have plenty left over, for Hashem has blessed His people." This follows what our Sages said in the Talmud, Tractate Shabbat (119a): "Tithe so that you will become wealthy."
Our Sages said in the Talmud, Tractate Ketubot (50a): "Rabbi Ila'a said: In Usha (a place), they established that one who gives away [to charity], should not give away more than a fifth," meaning, one should not give more than a fifth of their possessions to charity, lest they themselves end up needing charity.
Regarding the minimum measure, the Talmud states: "A person should never refrain from giving at least a third of a shekel annually." This means that the minimum amount required to fulfill the Torah commandment of charity is a third of a shekel per year, which is worth about seven grams of pure silver. However, it is clearly a very poor practice for someone to give only this meager amount, as we mentioned, because in places where Jewish scholars have authority, they should compel a person to give according to their ability, and undoubtedly Hashem will hold such a person accountable. But one who gives charity to the poor, especially one who supports Torah scholars, receives great reward, and through the power of charity, all kinds of harsh and evil decrees will be removed from them, for charity saves from death, as happened to the woman from Tzarfat in the time of Elijah the Prophet, who, because of a small cake she gave to Elijah, merited that her son who lay as if dead was revived, and she saw joy from him for many years.
Rulings of Rabbi Ovadia Yosef, courtesy of "Daily Halacha" website