Bar and bat mitzvah date calculator
From the Hebrew birth date.
How it’s worked out
Bar mitzvah at 13 and bat mitzvah at 12, on the Hebrew birthday. The Hebrew day begins the evening before. Born in Adar of a common year, or in Adar II, and the year is a leap year: Adar II. Born on a 30th that the year lacks: the 1st of the next month.
Source