Lent is forty days in every tradition and the same length in none of them. Rome runs Ash Wednesday to the evening of Holy Thursday — forty-four calendar days — and reaches forty by not counting the six Sundays, which are never fast days. Byzantium counts straight through, Sundays included, from Clean Monday to the Friday of the sixth week, and arrives at forty with Holy Week left over: Lazarus Saturday and Palm Sunday fall between the fast and the Passion, belonging to neither. The Copts keep fifty-five, a preparatory week and the forty and Holy Week together. So the two halves of the church can be fasting on the same day of the same year and be in different weeks of the same season.
The Typikon