Strict Jewish law requires that one should fast on the day of a parent's Yahrzeit. In practice, however the Rabbis do not insist on the observance of this custom, but encourage the relatives of the deceased to perform other mitzvoth, such as giving a donation to charity, in their name.

One explanation for fasting is that we compare our willingness to give up a part of ourselves on behalf of our parents with what our parents went through during our own childhood. What they imparted to us was by way of constantly putting aside personal gain. Our fast on their behalf can be regarded as a way of giving something to a soul who has no ability to receive anything physical.

Among Chassidic communities, instead of fasting, there is a custom for a person celebrating a Yahrzeit to bring drinks (usually whiskey or vodka) and cake to the synagogue to share with other members of the congregation after Shacharit the morning service. This snack is known as Tikkun (the Hebrew word means improvement, repair).

The custom has its roots in Jewish mysticism. One explanation is that when the congregants eat and drink, it is assumed that they will make the appropriate blessings. Since it is the deceased who is 'responsible' for these blessings being uttered, his/her soul receives additional credit, thereby becoming 'elevated' or 'improved'. Furthermore, the wording of the blessing on the drink is 'Blessed are You, God, King of the universe at whose word all things come into being', acknowledging that everything that happens in the celestial as well as the terrestrial realm occurs because God wills it."