Determining the day of the week for any day of the year.

The more rules you remember, the faster you can determine the week day:

• To avoid leap-year problems, the "year" runs from March through February.
• August 1 always defines the year's special day (e.g. in 2020 August 1 is Saturday).
• The last day of the preceding February is also the special day.

• Special days occur on most even numbered months on the same numbered day: 04/04, 06/06, 08/08, 10/10, 12/12.
• 05/09 and 09/05 are also special days.

• Some historical or religious events occur on the special day, such as June 6 (D-Day), October 31 (Hallowe'en), and December 26 (Boxing Day).
• Some national holidays are always on the special day, such as February 6 (New Zealand), May 9 (Russia, Europe), June 6 (Sweden), July 4 (USA), August 1 (Switzerland), and October 3 (Germany).
• Some friends and relatives will have birthdays, anniversaries, etc. on the special day.

• January and February of the next calendar year are the same as May and June.
• March and November are the same, with the special day an exact multiple of 7.
• April and July are the same.
• September and December are the same.