There are 14 possible year patterns (if one excludes 1752, the year when Great Britain and her colonies switched from the Julian to the Gregorian calendar, when 11 days were 'missed out' from September. However let us ignore such historical problems, otherwise other issues arise - such as before 1751 the New Year began on Lady Day (25 March) rather than 1 January).

The 14 possible year patterns are made from:

- 7 different days on which the year can start
- and for each, 2 ways the year can proceed (Leap Year, or Non-Leap Year).

Whitaker's Almanac refers to these 14 years by year letter, in the range
A to N.

Years B*,D*,F*,H*,J*,L*, and N* are Leap Years, '*' indicates a Leap Year in the rest of this page.

Years A,C,E,G,I,K, and M are Non-Leap Years

For the current period of interest:

Year | Year Type |
---|---|

1997 | G |

1998 | I |

1999 | K |

2000 | N* |

2001 | C |

2002 | E |

2003 | G |

2004 | J* |

Year start:

Year Type | Jan 1 falls on |
---|---|

A and B* | Sunday |

C and D* | Monday |

E and F* | Tuesday |

G and H* | Wednesday |

I and J* | Thursday |

K and L* | Friday |

M and N* | Saturday |

Year end:

Year Type | Dec 31 falls on |
---|---|

N* and A | Sunday |

B* and C | Monday |

D* and E | Tuesday |

F* and G | Wednesday |

H* and I | Thursday |

J* and K | Friday |

L* and M | Saturday |

An examples of each year type is:

A | B* | C | D* | E | F* | G | H* | I | J* | K | L* | M | N* |

1995 | 1984 | 1990 | 1996 | 1991 | 1980 | 1997 | 1992 | 1998 | 1976 | 1993 | 1988 | 1994 | 2000 |

Within my code, the value 'x%7' is used, where 'x' is *the day number of the year (1-366)* minus *the day of the week (1-7)*.

This is the date of the first Sunday in the year (except that '0' is used instead of '7').

The mapping between 'x%7' and the year type letter is:

x%7 | 0 | 1 | 2 | 3 | 4 | 5 | 6 |
---|---|---|---|---|---|---|---|

Year Letter | C/D* | A/B* | M/N* | K/L* | I/J* | G/H* | E/F* |

The sequence of year types is:

Year -1 | Year | Year +1 |
---|---|---|

L*/M | A | C/D* |

M | B* | E |

A/N* | C | E/F* |

A | D* | G |

B*/C | E | G/H* |

C | F* | I |

D*/E | G | I/J* |

E | H* | K |

F*/G | I | K/L* |

G | J* | M |

H*/I | K | M/N* |

I | L* | A |

J*/K | M | A/B* |

K | N* | C |

This information provided by Andrew Benham