Off the top of my head, the easiest (but definitely not prettiest or cleverest) would be to create a 2nd table based on the 1st

eg, assuming your 25 columns are from A - Y, with the required data in row1 and data from rows 2 onwards then in AA2 put 
=IF(A2>A$1,true,false)
then drag this along and down to fill the table then in the cell you want your percentage put: 
=COUNTIF("AA2:AY2",true)/25
You can then hide the columns containing the 2nd table