|| 684 || 687 |} 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. The months with a Friday the 13th are determined by the Dominical letter (G, F, GF, etc.) of the year. Years which begin on the same day of the week and are of the same type (i.e. common year or leap year), will have a Friday the 13th in the same months. This sequence, given here for 1900–2099, follows a 28-year cycle from 1 March 1900 to 28 February 2100: Frequency Although there is always at least one Friday the 13th per calendar year, it can be as long as 14 months between two Friday the 13ths. The longest period that occurs without a Friday the 13th is 14 months, either from July to September the following 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). On average, there is a Friday the 13th once every 212.35 days. Friday the 13ths occurs with an average frequency of 1.7218 per year or about 3477 since the year 1 CE. Frequency within a single year There can be no more than 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 1984, 2012, or 2040) (AG). In the 2000s, there were three Friday the 13ths in 2009, and two Friday the 13ths in 2001, 2002, 2006, and 2007. In the 2010s, there were three Friday the 13ths in 2012 and 2015, and two in 2013, 2017, 2018, and 2019. In the 2020s, there were two Friday the 13ths in 2020. There will also be three Friday the 13ths in 2026, and two in 2023, 2024, and 2029. The remaining years all have at least one Friday the 13th. For the details see the table below; this table is for the Gregorian calendar and