When a girl reaches the age of twelve, she becomes a bat mitzva. From this point forward, she is obligated to fulfill all of the mitzvot, just like any other adult woman.

The age at which girls become obligated in mitzvot is earlier than that of boys, due to their quicker physical and mental maturation. Some connect this halakha to the following talmudic statement: “The Holy One, blessed be He, granted a woman a greater level of understanding than that of a man” (Nidda 45b).

From the age of twelve, a girl must observe all the commandments that apply to adult women. She must eat matza on Passover, fast on public fast days such as Yom Kippur and Tisha BeAv, refrain from actions that violate the sanctity of Shabbat and festivals, and much more.

Likewise, from now on, her actions have halakhic ramifications for others. For example, until the age of twelve, when baking bread, she may not be the one to fulfill the mitzva of setting aside a portion of the dough [halla]. When she turns twelve, she can fulfill this mitzva, which thereby renders the bread permitted for all to eat. She is also permitted to recite Kiddush for other women, enabling them to fulfill their obligation by listening to her.

Further reading: For more on the mitzva and procedure of separating halla, see p. 547.

In the past, it was not customary to mark a girl’s bat mitzva with a festive celebration. It seems that this was due to the domestic nature of girls’ lives in those days. In modern times, it has become common to hold a bat mitzva celebration. At a bat mitzva celebration it is fitting for the young woman to share some Torah thoughts, and thereby imbue the event with religious content.