This gets us back to the extra month. Within a 19year cycle a 13th month is added on the 3rd, 6th, 8th, 11th, 14th, 17th, and 19th years of that cycle. This month is called Adar I or Adar Alef. It occurs just before Adar (which is called Adar II or Adar Bet in a leap year). While this system is perplexing, it does work to keep the calendar in order. In English these are called leap years in Hebrew they are called Shanah Me’uberet – a pregnant year.
So how do we handle the birthdays and anniversaries produced during a Shanah Me’uberet? The answer lies in a famous Jewish riddle…
Two twin boys are born only minutes apart, but 13years later their Bar Mitzvahs are celebrated 29 days apart and the second born celebrates first. How can that be?
The twins were born in a Shanah Me’uberet. The first son was born just before sunset on 30 Adar I and the second son was born just after sunset on 1 Adar II. In a regular year, such as the boys’ Bar Mitzvah year, each twin celebrates his birthday on the corresponding day in the regular month of Adar.
Therefore, the younger twin will have his Bar Mitzah first on the 1st of Adar and the older twin will have his Bar Mitzvah 29 days later on the 30th of Adar.