How many Leap Days occur in 400 years?
Leap year starting on Saturday followed by a leap year and the other a leap year followed by a common year. Leap years that begin on Saturday, along with those that start on Monday or Thursday, occur least frequently: 13 out of 97 (≈ 13.4%) total leap years in a 400-year cycle of the Gregorian calendar. Their overall occurrence is thus 3.25% (13 out of 400). Century leap years are always leap years starting on Saturday and February 29 is always on Tuesday. Like all leap year types, the one starting with 1 January on a Saturday occurs exactly once in a 28-year cycle in
Century leap year thus the leap day February 29 in those years always falls on a Tuesday (dominical letter BA). The Gregorian calendar yields an average year that currently tracks the annual revolution period of the Earth more closely than the older Julian calendar, in which every fourth year (including end-of-century years) is a leap year. The Julian formula adds too many leap days (3 every 400 years), causing the Julian calendar to drift gradually with respect to the astronomical seasons. Over time, natural events such as the spring equinox began to occur earlier and earlier in the Julian calendar. The Gregorian calendar