Add an extra column at N called % increase & input the % increase

then in your month columns don' call them jan feb etc call them 31/1/05 ,
28/2/05 etc
then put this formula in 31/1/05 column & drag across to 31/12/05 column

IF(Q1$K$3,($H$3+($H$3*$N$3))/12,$H$3/12)


the columns should read like this

H I J K L
M N O - AA
Act base Anticip Date of Increase Actual Month %
Pay Increase last incr date Incr amt Base
increase 31/3/05 etc

35000 35700 3/01/05 01/03/05 58.33 2916.67 2%


Note the absolute references in the formula ( $ )