In the old days, tsukinami-no-matsuri seemed to be held monthly, however, it was determined in the "Engishiki" (an ancient book for codes and procedures on national rites and prayers) to hold tsukinami-no-matsuri on 11th day of June and December.
古くは毎月行われたようであるが、『延喜式』において6月と12月の11日に行うことが規定された。