And this stone, which I have set up as a pillar, shall be God’s abode; and of all that You give me, I will set aside a tithe for You.”

WhenMar Ukvawas dying, he said: Bring me my charity records. He found that it was written there that he had given seven thousand fine, siankei, i.e., gold, dinars, to charity. He said: My provisions are light, and the way is far. This meager sum is insufficient for me to merit the World-to-Come. He got up and spent half of his remaining money on charity. The Gemara asks: How did he do this? But didn’t Rabbi Ilai say: In Usha they instituted: One who spends money on charity, he should not spend more than one-fifth of his money for this purpose. The Gemara answers: This restriction on giving too much charity applies only while he is alive, because perhaps he will descend from his holdings and become destitute. Therefore, for his own financial security, he should never distribute more than one-fifth. But after death, we have no problem with it. One need not save money in his estate anymore.

§ Apropos the ordinances instituted by the Sages in Usha, the Gemara cites another one. Rabbi Ile’a said: In Usha the Sages instituted that one who dispenses his money to charity should not dispense more than one-fifth. That opinion is also taught in a baraita: One who scatters should not scatter more than one-fifth, lest he render himself destitute and need the help of other people. And an incident occurred involving a certain individual who sought to dispense more than one-fifth of his property as charity, and his friend did not let him act upon his wishes. And who was this friend? Rabbi Yeshevav. And some say that Rabbi Yeshevav was the one who wanted to give too much charity, and his friend did not let him do so, and who was the friend? Rabbi Akiva.Rav Naḥman said, and some say it was Rav Aḥa bar Ya’akov who said: What is the verse that alludes to this maximum amount of charity? “And of all that You shall give me, I will surely give a tenth of it [aser a’asrenu] to You” (Genesis 28:22). The double use of the verb that means to donate one-tenth indicates that Jacob, who issued this statement, was actually referring to two-tenths, i.e., one-fifth. The Gemara asks: But the latter tenth is not similar to the first tenth, as it would be one-tenth of what remained after the first tenth had been removed. Consequently, the two-tenths would not equal one-fifth of the original total. The Gemara answers that Rav Ashi said: Since the verse could have said: I will surely give one-tenth [aser a’aser], and instead stated: “I will surely give a tenth of it [aser a’asrenu],” it thereby alludes to the fact that the latter tenth is like the first one.

The amount of charity one should give is as follows: if one can but afford, let him give as much as is needed. Under ordinary circumstances, a fifth of one's property is most laudable. To give one-tenth is the average disposition. But to give less than one-tenth is niggardly. When the Rabbis said a "fifth" they meant a fifth of the property the first year only and a fifth of the profits in succeeding years.
RMI.—But a man should not squander more than one-fifth to charity, so that he might not himself become a public charge.This refers only to his lifetime. Of course, at the time of death one may leave for charity as much as he pleases.

(1)One must pursue beautification of the mitzvah when buying an etrog: If one bought an etrog that can just barely fulfill the obligation, i.e. if it was exactly an egg-size, and afterward found a bigger one, it is a mitzvah to pay up to a third more than the price of the first to swap it out for the nicer one. There is one who says that if there are two etrogs available for purchase, one nicer than the other, the nicer one should be purchased if it is not more than a third more expensive than the other one. RAMA: Somebody who doesn't have an etrog or some other [objected associated with a] mitzvah whose time will elapse need not dispense much wealth on it, as they said, "One who dispenses [money to charity] should not dispense more than one-fifth [of their wealth]" [Ketubot 50a], even with respect to a mitzvah with a time that will elapse (Ros"h, Rabbeinu Yerucham 13:2). This specifically applies to a positive mitzvah. However, regarding a negative mitzvah, one should spend all of their wealth rather than sin (Rashb"a and Raavad). See the end of 658 in the Rama.

'וכל אשר תתן לי וגו, “and all that You will give to me, etc.;” Yaakov promised to tithe all the money (material goods) that he would acquire with the help of G–d. (B’reshit Rabbah, 70,7) A heretic once asked Rabbi Yoshua son of Levi, where the Torah reported that Yaakov kept this promise. He was answered that Yaakov declared this tithe “sacred,” i.e. he gave it to the treasury of religious institutions. Thereupon the heretic wanted to know what this tithe consisted as precisely seeing that Yaakov was not a wealthy man. He was told that Yaakov made all his newly born animals pass under a gate, and every tenth animal he declared as holy, i.e. not to be used for secular needs. In the Talmud this procedure is called: מעשר בהמה, “tithe from livestock.” [Since Yaakov did not plant crops, not owning any arable land in the land of Canaan (except one small field near Sh’chem from which he moved away before it could produce a crop), he could not tithe his crops. The version in my edition of B’reshit Rabbah is slightly different but the point is made that Yaakov certainly did not default on his vow. Ed.]

עשר אעשרנו לך, “I will give two tithes of it to You.” Yaakov kept his promise to give a tithe of everything that was his, including even his children. [This has been discussed in connection with 27,19. Ed.] Our verse forms the basis of a Talmudic statement in Ketuvot 50 that even someone who dispenses charity very generously should not disburse more that one fifth of his wealth so as not to risk becoming a charge on charity himself. Yaakov serves as the example seeing he tithed 20% of his wealth.