On the day he turns thirteen, a boy becomes a bar mitzva. Bar is the Aramaic equivalent of the Hebrew word ben, which literally means “son,” but is also used to indicate the ability to do something, or even more broadly as a general manner of defining a status. Thus, bar mitzva means that the individual is now defined as someone who is subject to mitzvot. This expression reflects the profound connection that is formed between the maturing adolescent and the mitzvot that he will begin to observe.

As soon as a boy reaches the age of thirteen, he is obligated to fulfill all of the Torah’s commandments that apply to him, just like a full-fledged adult. For example, he must fast on public fast days, such as Yom Kippur and Tisha BeAv. He is similarly required to dwell in a sukka on Sukkot, eat matza on Passover, wear ritual fringes [tzitzit], and observe Shabbat.

Along with these obligations, the new bar mitzva also acquires the halakhic privileges of adulthood. He may now be counted for a minyan, the quorum of ten men required for public prayer and some other ritual matters. He may even serve as the prayer leader [hazan] in the synagogue. He may recite Kiddush on Shabbat and festivals and thereby facilitate the fulfillment of the mitzva for those who hear him. And of course, he is entitled to be called up to the Torah reading.

It is important to note that one becomes bar mitzva on his date of birth in the Jewish calendar, not on his birthday according to the Gregorian calendar. These two dates will not coincide, and there is often a gap of days or even weeks between them. One must therefore consider his son’s Hebrew birthday when determining the date of the bar mitzva.

In this context, it is important to note that while a new day in the Gregorian calendar begins at midnight, the date in the Jewish calendar begins at nightfall. Consequently, if one is determining the Hebrew birthday by looking it up in a calendar based on the Gregorian date, one must also know the time of day when the child was born. For example, if he was born at night, the Hebrew date that appears on the calendar for that Gregorian date would actually be the day before his birthday, as the date had already changed in the Jewish calendar by the time he was born.

Therefore, one who was born between sunset and midnight must move his birthday one day later, after converting the Gregorian date to the Hebrew date. For example, if he was born on March 23, 2004, a conversion table will give the date of the first of Nisan 5764. Nevertheless, as he was born after nightfall, his birthday is actually the second of Nisan, and he becomes bar mitzva on that date.

There are several websites that help one convert the Gregorian date to the Hebrew one, and they include the option of specifying the time of birth, which helps one find the correct date without difficulty.

There are some instances that require special attention when determining the date of a bar mitzva:

In the Jewish calendar, seven of every nineteen years are leap years, in which an additional month is added. In leap years there are two months called Adar. If a child was born in the month of Adar in a regular year and his bar mitzva is in a leap year, he becomes bar mitzva in the second Adar rather than the first. With regard to birthdays, the second Adar is considered the primary month of Adar.

However, if one was born in the first Adar in a leap year and the year of his bar mitzva is also a leap year, he becomes bar mitzva in the first Adar. Similarly, if he was born in the second Adar in a leap year, and he becomes bar mitzva during a leap year, he will be considered a bar mitzva in the second Adar.

If a child was born during either of the two months of Adar in a leap year and the year of his bar mitzva is a regular year with only one Adar, he will become bar mitzva during the month of Adar.

There are two other dates that exist in only some years: the thirtieth of Marheshvan (the first day of Rosh Hodesh Kislev) and the thirtieth of Kislev (the first day of Rosh Hodesh Tevet). The months of Marheshvan and Kislev can contain twenty-nine or thirty days, depending on the year. If one was born on either of these two dates and it does not exist in the year that he becomes bar mitzva, he is considered a bar mitzva on the following date. Consequently, if he was born on the thirtieth of Marheshvan he will become bar mitzva on the first of Kislev, and if he was born on the thirtieth of Kislev he will become bar mitzva on the first of Tevet.