In the Roman Rite, the definition of Lent varies according to different documents. While the official document on the Lenten season, Paschales Solemnitatis, says that "the first Sunday of Lent marks the beginning of the annual Lenten observance", the Universal Norms on the Liturgical Year and the Calendar says, "The forty days of Lent run from Ash Wednesday up to but excluding the Mass of the Lord's Supper exclusive." The first source represents a period of 40 days and the second a period of 44 days, because both sources agree that the end of Lent comes the evening of Holy Thursday, before the Mass of the Lord's Supper. Though some sources try to reconcile this with the phrase "forty days" by excluding Sundays and extending Lent through Holy Saturday no official documents support this interpretation.
In the Ambrosian Rite, Lent begins on the Sunday that follows what is celebrated as Ash Wednesday in the rest of the Latin Catholic Church, and ends as in the Roman Rite, thus being of 40 days, counting the Sundays but not Holy Thursday. The day for beginning the Lenten fast is the following Monday, the first weekday in Lent. The special Ash Wednesday fast is transferred to the first Friday of the Ambrosian Lent. Until this rite was revised by Saint Charles Borromeo the liturgy of the First Sunday of Lent was festive, celebrated in white vestments with chanting of the Gloria in Excelsis and Alleluia, in line with the recommendation in Matthew 6:16, "When you fast, do not look gloomy"