If I get a tax return refund for (having given) charity, can I consider myself as having tithed? Or should I re-tithe the return?

Your question is a great one because you are thinking diligently not only about your commitment to your government but your commitment to religious obligations (and consequently helping others) as well. As my Reform colleague on this site, Rabbi Mark Washofsky stated, according to Rabbi Moshe Feinstein, you don’t have the obligation to tithe based on your tax return, since you fulfilled your obligation of giving 10% already. That being said, you might ask yourself-did I give 10% based on my gross or net income? If you “only” gave it based on the net income (after taxes were withheld), and still received a refund, you could make the decision that you should have given it based on the gross income and therefore give a bit more now that you have the funds. But that is for you to decide.

I believe that your question concerning taxes and tithing is well intended.  However, I feel that it is somewhat problematical from the standpoint of Judaism and the Halakhah (Jewish Law).

How so?  Your premise assumes that tithing in its narrow sense, perhaps in some societal way is mandated in Judaism.

Yes, it is true that in former times Judaism required a very structured system of Terumot and Ma’aserot for upkeep of the Kohanim (priests) and the Levites in the Land of Israel.  However, with the Destruction of the Temple in Jerusalem in 70 C.E. and the subsequent dispersion of the Jews from their Land, this system fell into disuse, at least as formerly understood.

In a technical sense, Jews continue to “tithe” the produce of Israel, however, these tithings are no longer used for their original intended purpose, until sometime in the future when there will, with G-d’s help, be a full restoration of the Jewish People in the Land.

There are numerous mitzvot in both the Written and Oral Torah, that relate to what in English is called “charity.”  Some of these include Gemillut Hasadim (Deeds of Loving-kindness), Tzedakah (Righteous Giving), Ma’aser Ani (Tithe for the Poor), Peah—Leket—Peret—Shikhehah (Leaving Portions Behind and Gleanings during Harvesting, etc.) and Matanot La-Evyonim (Gifts for the Needy).

While I believe that there is no absolute directive when it comes to generosity in giving to the needy and your relationship to paying taxes and receiving tax benefits, Jewish sources can be beneficial in considering how to proceed.

Maimonides (12th century, Egypt) describes the commandment of the Corner of the Field—Peah.  He writes in his Mishneh Torah, “Hence you learn that four gifts are reserved for the poor in the vineyard: single grapes, young grapes, Peah (Corner of the Field), and forgotten grapes; three gifts in grain: gleanings, the forgotten sheaf, and Peah; two in trees: the forgotten fruits, and Peah. (Laws of Gifts to the Poor, Chapter 1, Law 7)

He continues describing the Mitzvah of Peah, “Biblically it has no prescribed limit….  Rabbinically, however, Peah should not be less than one-sixtieth of the harvest, whether in the Land of Israel or in the Diaspora.  One should add to the one-sixtieth according to the size of the field and the number of the poor and the yield of the harvest….  If he sowed little and harvested much, having prospered, he should increase it in accord with the blessed crop.  Whoever increases the rate of Peah will receive a higher reward.  There is no prescribed limit to this increase. ” (Law 15)

The Mishnah as quoted in the traditional Jewish Prayer Book–the Siddur—offers sound advice for us all, “These are the things for which there is no fixed measure: the corner of the field, first-fruits, appearances before God [on festivals], acts of kindness and the study of Torah.” (Peah 1:1)

I would think that given the attention that the Torah devotes to the subject of Deeds of Loving-kindness in their manifold manifestations, “tithing”—meaning giving one-tenth of one’s taxable income to charitable causes would not meet with even a minimum of what is to be expected of each and every Jew.  But, it’s a good start and may G-d give us the wherewithal, strength and will to go above and beyond, to do His bidding.