The First Sunday Doomsday Algorithm is the simplest way to calculate the day of the week for any date in your head.<p><a href="http:&#x2F;&#x2F;firstsundaydoomsday.blogspot.com" rel="nofollow">http:&#x2F;&#x2F;firstsundaydoomsday.blogspot.com</a><p>It brings together a bunch of great mnemonics, like the new &quot;odd+11&quot; rule for calculating the 2-digit year code, as well as Conway&#x27;s classic &quot;I work 9-5 at the 7-11&quot; for the month code.