Is there a calculator existing to find how many Fri the 13Th are in any given year?

Answer 1

There are only 14 calendars - all years match one of them.

A year is either a 'leap year', or a 'common year'. So two calendars are needed to cover all years which start on a Sunday, two for the years which start on a Monday, and so on.

If a common year starts on a Sunday then the 13th of January and October are Fridays

This covers 1905 1911 1922 1933 1939 1950 1961 1967 1978 1989 1995 2006 2017 2023 2034 2045 2051 2062 2073 2079 2090

If a common year starts on a Monday then the 13th of April and July are Fridays

This covers 1906 1917 1923 1934 1945 1951 1962 1973 1979 1990 2001 2007 2018 2029 2035 2046 2057 2063 2074 2085 2091

If a common year starts on a Tuesday then the 13th of September and December are Fridays

This covers 1901 1907 1918 1929 1935 1946 1957 1963 1974 1985 1991 2002 2013 2019 2030 2041 2047 2058 2069 2075 2086 2097

If a common year starts on a Wednesday then the 13th of June is a Friday

This covers 1902 1913 1919 1930 1941 1947 1958 1969 1975 1986 1997 2003 2014 2025 2031 2042 2053 2059 2070 2081 2087 2098

If a common year starts on a Thursday then the 13th of February, March and November are Fridays

This covers 1903 1914 1925 1931 1942 1953 1959 1970 1981 1987 1998 2009 2015 2026 2037 2043 2054 2065 2071 2082 2093 2099

If a common year starts on a Friday then the 13th of August is a Friday

This covers 1909 1915 1926 1937 1943 1954 1965 1971 1982 1993 1999 2010 2021 2027 2038 2049 2055 2066 2077 2083 2094 2100

If a common year starts on a Saturday then the 13th of May is a Friday

This covers 1910 1921 1927 1938 1949 1955 1966 1977 1983 1994 2005 2011 2022 2033 2039 2050 2061 2067 2078 2089 2095

If a leap year starts on a Sunday then the 13th of January, April and July are Fridays

This covers 1928 1956 1984 2012 2040 2068 2096

If a leap year starts on a Monday then the 13th of September and December are Fridays

This covers 1912 1940 1968 1996 2024 2052 2080

If a leap year starts on a Tuesday then the 13th of June is a Friday

This covers 1924 1952 1980 2008 2036 2064 2092

If a leap year starts on a Wednesday then the 13th of March and November are Fridays

This covers 1908 1936 1964 1992 2020 2048 2076

If a leap year starts on a Thursday then the 13th of February and August are Fridays

This covers 1920 1948 1976 2004 2032 2060 2088

If a leap year starts on a Friday then the 13th of May is a Friday

This covers 1904 1932 1960 1988 2016 2044 2072

If a leap year starts on a Saturday then the 13th of October is a Friday

This covers 1916 1944 1972 2000 2028 2056 2084