Bar mitzvah, bat mitzvah: which Hebrew date?
Religious adulthood is not counted in civil years: a boy becomes bar mitzvah at thirteen Hebrew years, a girl bat mitzvah at twelve, on the day of the Hebrew birthday. You still need the right Hebrew birth date, and three cases trip up almost everyone.
The rule
Thirteen years and a day, twelve years and a day
“At thirteen, the commandments,” teaches the Mishnah (Avot 5:21). The law makes it precise: a boy comes of age at thirteen full years and one day, a girl at twelve full years and one day (Shulchan Aruch, Orach Chaim 55:9; Rambam, Laws of Marriage 2:1-2). The count is made in years of the Hebrew calendar, starting from the Hebrew birth date.
In practice: born on 12 Kislev 5774, a boy becomes bar mitzvah on 12 Kislev 5787. The ceremony is usually held on the following Shabbat, or on the day itself if the birthday falls on a Monday, a Thursday or Shabbat, the days the Torah is read.
So everything rests on one thing: the exact Hebrew date of birth. And that is where it gets tricky.
Case no. 1
Born in the evening: it is no longer the same day
The Hebrew day begins at sunset. A child born at 9 PM on March 3 was born, for the Hebrew calendar, on the day after March 3. Converters that only ask for the date are off by one day for every evening birth, and one day can mean another month, so another week for the bar mitzvah.
You need the time and the place: the sun does not set at the same minute in New York, Los Angeles or Jerusalem. The calculator takes both into account.
Case no. 2
Born in Adar: Adar I or Adar II?
Seven years out of nineteen have two months of Adar. The rule of the Rema (Orach Chaim 55:10): born in Adar of an ordinary year, if the year of the bar mitzvah is a leap year, it falls in Adar II. Born in Adar I, it falls in Adar I; born in Adar II, in Adar II. And if the year of the bar mitzvah has only one Adar, that is the month, whatever the Adar of birth.
Case no. 3
Born on the 30th of a month that only has 29 days
Cheshvan and Kislev have sometimes 29, sometimes 30 days. Born on 30 Cheshvan or 30 Kislev, if the year of the bar mitzvah has only 29 days in that month, the bar mitzvah falls on the 1st of the next month (Mishnah Berurah on Orach Chaim 55). A rare case, but one that moves the date by a whole month if it is overlooked.
And you
Date, time and place: the exact Hebrew date, sunset included, and the next twelve Hebrew birthdays.
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Frequently asked
In four answers
At what age is a boy bar mitzvah?
At thirteen full Hebrew years and one day, on his Hebrew birthday, not his civil birthday (Mishnah Avot 5:21; Shulchan Aruch, Orach Chaim 55:9).
At what age is a girl bat mitzvah?
At twelve full Hebrew years and one day, on her Hebrew birthday (Rambam, Laws of Marriage 2:1-2).
How do you calculate a bar mitzvah date?
Convert the birth date into a Hebrew date, taking the time of birth into account (the Hebrew day begins at sunset) and the place, then add thirteen Hebrew years, twelve for a bat mitzvah. The ceremony is usually held on the following Shabbat.
Born in Adar: which Adar for the bar mitzvah?
Born in Adar of an ordinary year, if the year of the bar mitzvah is a leap year, it falls in Adar II (Rema, Orach Chaim 55:10). Born in Adar I, it falls in Adar I; born in Adar II, in Adar II.