Q. Is there an obligation to give maaser kesafim (tithes of one tenth) of one’s earnings to the poor?
A. Shulchan Aruch (248: 1) rules that everyone is obliged to give tzedaka, even one who himself depends on charity to survive.
Rambam (H. Maatonos Aniyim 7: 5), writes that the most desirable way of performing the mitzvah of charity is to give up to a fifth of one’s financial resources. Giving one-tenth is an ordinary measure; giving less reflects stinginess.
The first reference of maaser kesafim appears in the narrative of Avraham Avinu and Yaacov.
On the statement of Yaakov Avinu: “And all that You will give me, I shall surely tithe for You” (Bereishis 28:22), Baalei Tosafos quote a Midrash: “Yaakov Avinu enacted the tithing of one’s wealth.”
Poskim disagree as to what kind of mitzva this is. Some consider it a biblical mitzvah, however, most see it as either a rabbinic enactment derived from the mitzva of tithing crops, (Taz Y.D, 331: 32) or as only a minhag or tradition.
Tosafos (Taanis 9a D’H Aser) quotes from Sifri, that the instruction to tithe is not limited to the produce of the field, but applies rather to all income. Based on Tosafos, Chavas Yair, (224) writes that the concept of giving maaser is an obligation. Bach (Y.D. 331: 19) writes that it is permitted to use one’s maaser money to pay off debts. This seems to indicate that giving maaser is not considered an obligation.
Similarly, Pischei Teshuva (321: 12) quotes Maharam M’Rothenburg that there is no obligation even a Rabbinical one to give maaser kesafim, only a minhag shel mitzva/
Many see maaser kesafim as part of the general mitzvah of tzedakah, or charity. (Sheilas Yaavetz 1: 3).
On question 1783 regarding becoming obliged on maaser kesafim by accepting it as a neder or promise we wrote: Horav Shlomo Miller’s Shlit’a opinion is that if at the time one accepted or took upon himself the giving of maaser, he had in mind to include all tzedaka donations and mitzva expenditures they will be included in the sum total of the maaser for that year.
If one keeps his giving of maaser specifically for tzedaka for the needy, however he declared from the onset that everything is being done “beli neder,” without accepting any oath or vow, he may now include also the above.
If one is uncertain whether the original maaser neder was only for tzedaka purposes or it included also all mizvos expenditures, the Rov maintains that one should be matir neder or annul the vow done, and specify that all subsequent actions are done “beli neder” and include mitzva dues.”
Horav Shlomo Miller’s Shlit’a opinion on the obligation of maaser kesafim is similar to many Poskim, that it is a mitzva and not a chiyuv.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a