variance analysis

cell A1 is 10 input
cell B1 is 5 input
cell c1 is 5 formula A1 - B1

I only want to look at variances that are greater than or less than 25% of
cell A1 I can create the formula and it works but if the variance is
negative because A1 is less than B1 then I can't get it to show a
variance..only 0

Any help would be appreciated...