Ta'anis Bechoros: The Fast of the Firstborn

This fast day is only kept by firstborns over the age of 13, in commemoration of the fact that they were spared by G-d from the death of all the firstborn in Egypt. This applies whether the person is a firstborn of only one parent or both.

According to some customs, firstborn women also fast, since they too were included in the threat of death and the salvation. According to other customs, the women do not have to fast, since commemorating the past via positive action is a responsibility that devolves on adult males on behalf of everyone else (women and minors). If the women should choose to fast, they are permitted to do so.

From Chabad.org:

Firstborn males over the age of Bar Mitzvah (13) are obligated to fast on the 14th of Nissan, in recognition of the fact that during the "Plague of the Firstborn" (which occurred at midnight of Nissan 15) G-d "passed over" the Jewish firstborn when He killed all firstborn Egyptians. If there is a firstborn male in the family under 13, the obligation to fast rests with the father. The prevailing custom, however, is for the firstborn to exempt themselves from the obligation to fast by participating in a seudat mitzvah (a meal marking the fulfillment of a mitzvah), such as a siyyum – a festive meal celebrating the conclusion of the study of a section of Torah).

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It is an ancient and widespread custom for the firstborn to fast on the day before Passover. This commemorates the miracle which spared the firstborn Jewish sons from the plague which struck down the firstborn sons of the Egyptians.

By right, this fast should be held on the anniversary of the day on which the miracle occurred: on the night of the fifteenth of Nissan. However, since the fifteenth is already Passover, and we do not fast on Festival days, the fast is pushed back to the fourteenth.

There is an additional reason why we fast specifically on the fourteenth. The firstborn of the Jews were saved in Egypt because they humbled themselves before G‑d, admitting and declaring that all greatness, power, and sovereignty are His alone.

This stood in contradistinction to the Egyptians who, filled with foolish pride and egotism, declared: "I am, and besides me there is none other."

Thus, the fast on the fourteenth of Nissan commemorates the fact that the firstborn of Israel humbled themselves on that day and accepted the yoke of G‑d's sovereignty. Abstention from food and drink is a sign of a heart subdued before G‑d.

There are different customs that are associated with this fast. Some maintain that every firstborn, male and female, whether the firstborn is that of the mother or of the father, must fast.

If there are no children, then the oldest member of the household must fast. They base this on the fact that there was no Egyptian household that was spared from the plague, every household in Egypt was struck whether there was a firstborn son or not. We commemorate, therefore, that all of the Jewish households were miraculously spared.

Others maintain that the obligation to fast applies only to firstborn males.

There are those who hold that the firstborn sons who are fasting should not fast for the entire day, in order not to enter the Festival suffering, and thus should eat a small amount before the Festival begins.

This fast is treated leniently. Thus, if there is a festive meal held that is connected with a mitzvah, for example, the celebration of a circumcision or of a siyum (the completion of a tractate of the Talmud) the firstborn son participates in the meal rather than fasting.

It is therefore customary to arrange for a siyum to take place in the synagogue after morning prayers on the fourteenth of Nissan. The firstborn sons who are present participate in this festive meal and, having broken their fast, may continue to eat for the rest of the day.