section_path: Months/Ayyám-i-Há
section_name: Ayyám-i-Há
paragraph_text: Ayyám-i-Há
  
  The introduction of intercalation marked an important break from Islam, as under the Islamic calendar the practice of intercalation had been specifically prohibited in the Qurʼan.
  
  The number of the intercalary days is determined in advance to ensure that the year ends on the day before the next vernal equinox. This results in 4 or 5 intercalary days being added. These days are inserted between the 18th and 19th months, falling around the end of February in the Gregorian calendar. The number of days added is unrelated to the timing of the Gregorian leap year.