The solemnity of the Annunciation of the Lord, celebrated nine months before Christmas, is assigned to March 25 on the Church’s General Calendar. But, on occasion, March 25 might fall on a day that would trigger a transfer of the solemnity.
Such liturgical shuffling is guided by a document promulgated after the reform of the Church’s calendar following the Second Vatican Council. General Norms for the Liturgical Year and the Calendar, promulgated by Pope Paul VI in 1969, ranks various liturgical celebrations according to an established precedence or order of importance and significance. The General Norms states that the Sundays of Lent and the days of Holy Week take precedence liturgically, even over feasts of the Lord — which is the type of feast the Annunciation is classified as.
Accordingly, then, if March 25 is on a Sunday of Lent, then the solemnity is observed on the following date applicable, which would most often be on March 26.
If March 25 lands during Holy Week or during the Easter octave (the week following Easter), however, then the Annunciation is transferred to the first Monday after the Easter octave. Therefore, this year, since March 25 is Holy Monday on the Roman calendar, the liturgical celebration of the Annunciation will be observed on Monday, April 8.
Additionally, on the solemnity of the Annunciation — just as on Christmas — the ministers and faithful genuflect during the Nicene Creed when the Lord’s Incarnation is referenced: “and by the Holy Spirit was incarnate of the Virgin Mary, and became man.”