In row 1 I have Jan to Dec - a header row
in row 2 I have a value directly under each date cell - the amount per month

in row 3 I need the percentage value of row2 over the year

ie if just using 4 months (I will be using 12 though)
Jan Feb March Apr month
5 5 20 20 Value
10 10 40 40 percentage of total year

I hope thats clear - many thanks