Tradition celebrates the event as a liturgical feast in the General Roman Calendar and in most Anglican liturgical calendars on 8 September, nine months after the solemnity of her Immaculate Conception, celebrated on 8 December. The feast is also included in the Tridentine Calendar for 8 September. This date is also used in the Western Rite Orthodox Church.
The Byzantine Rite Orthodox likewise celebrate the Nativity of the Theotokos on 8 September. The Syriac Orthodox Church, like its closely related sister church, the Byzantine Rite Antiochian Orthodox Church, also celebrates the feast on 8 September. For churches using the old Julian Calendar for liturgical purposes September 8 falls on September 21 of the Gregorian Calendar. In other words, “Old Calendar” Churches, such as the Russian Orthodox Church, still celebrate the Nativity of the Theotokos on the 8th, but the day is actually the 21st according to the everyday calendar used by society at large.
The Armenian Apostolic Church also uses the traditional date of 8 September. Yet the Coptic Orthodox and Ethiopian Orthodox Christians celebrate it on May 9 (1 Bashans, EC 1 Ginbot).