section_path: Components/Months/Justification for leap months
section_name: Justification for leap months
paragraph_text: Justification for leap months
  
  The Bible does not directly mention the addition of leap months (also known as "embolismic" or " intercalary " months). The insertion of the leap month is based on the requirement that Passover occur at the same time of year as the spring barley harvest (aviv). (Since 12 lunar months make up less than a solar year, the date of Passover would gradually move throughout the solar year if leap months were not occasionally added.) According to the rabbinic calculation, this requirement means that Passover (or at least most of Passover) should fall after the March equinox. Similarly, the holidays of Shavuot and Sukkot are presumed by the Torah to fall in specific agricultural seasons.
  
  Maimonides, discussing the calendrical rules in his Mishneh Torah (1178), notes:
  
  By how much does the solar year exceed the lunar year? By approximately 11 days. Therefore, whenever this excess accumulates to about 30 days, or a little more or less, one month is added and the particular year is made to consist of 13 months, and this is the so-called embolismic (intercalated) year. For the year could not consist of twelve months plus so-and-so many days, since it is said: "throughout the months of the year", which implies that we should count the year by months and not by days.