Originally, Kagamibiraki was held on January 20 (by the lunar calendar) after the Lunar New Year (January 15 (by the lunar calendar)), which was at the end of matsunouchi (the first seven days of the year in which matsu kazari (pine decorations) were displayed).
元々は松の内が終わる小正月（1月15日(旧暦)）後の1月20日(旧暦)に行われていた。