how do i get annual percentage difference reports in excel

[Guest]

i'm looking to compare two sets of figures for year on year accounts and
would like to ahve the percentage difference calculated whether it be
positive or negative, i.e. whether sales have increased or fallen on that
week compared to the same week last year.

i could do this with a calculator and do it manually but i have a lot of
data to crunch and need a helping hand

thanks

 

[Ian]

=(Thisyearcellref-Lastyearcellref)/Lastyearcellref

Format the result as %