Friday the 13th etc.) of the year. Any month that starts on a Sunday contains a Friday the 13th, and there is at least one Friday the 13th in every calendar year. There can be as many as three Friday the 13ths in a single calendar year; either in February, March and November in a common year starting on Thursday (such as 2009, 2015 or 2026) (D), or January, April and July in a leap year starting on Sunday (such as 2012) (AG). The longest period that occurs without a Friday the 13th is 14 months, either from July to September the following
Friday the 13th year being a common year starting on Tuesday (F) (e.g. 2001/02, 2012/13 and 2018/19), or from August to October the following year being a leap year starting on Saturday (BA) (e.g. 1999/2000 and 2027/28). The shortest period that occurs with a Friday the 13th is just one month, from February to March in a common year starting on Thursday (D) (e.g. 2009, 2015 and 2026). Each Gregorian 400-year cycle contains 146,097 days (with 97 leap days) or exactly 20,871 weeks. Therefore, each cycle contains the same pattern of days of the week and thus the same pattern of Fridays that