Can anyone tell me in which year I could accurately use a 2004 calendar again please, and what is the method used to work that out?
Thank you.

Found the info I was looking for here. http://webexhibits.org/calendars/yea...l#Anchor-22685

2009

Method...

leap: mod(366,7)= 2
not leap: mod(365,7)= 1

leap year : [ mod(year,4)=0 and mod(year,100)<>0 ] or mod(year,1000)=0

Jan 1 , 2004 : Thursday 366 +2
Jan 1 , 2005 : Saturday 365 +1
Jan 1 , 2006 : Sunday 365 +1
Jan 1 , 2007 : Monday 365 +1
Jan 1 , 2008 : Tuesday 366 +2
Jan 1 , 2009 : Thursday...

Jan 1 , 2015 : Thursday...
Jan 1 , 2026 : Thursday...
Jan 1 , 2032 : Thursday...
Jan 1 , 2037 : Thursday...

You can write a program to do this (I use Excel)...