The Perpetual Calendar
On this web site you will find how to
calculate (in your head) the day of the week of any given
date, in any century.
It has been the endeavour of scholars for
centuries to devise a simple formula for calculating a
The Marais Formula was coined and developed
by a South African, Etienne A. Marais, in Johannesburg in 1991
and simplifies the calculation of a perpetual calendar. It
utilizes a calendar key that makes it possible for a person
with basic mathematical skills to do seemingly intricate
mental calculations and produce astounding answers. By
reading through this web site and practising the methods you
will soon be able to do the whole calculation within a few
seconds, in your head.