Calculations on some columns

Hi, there! 

I have a pivot grid with a column field which is Types of budgets, there are 3 in the SQL query: initial budget, real budget, executed value. I want two calculated fields, namely the percentage difference between the initial budget vs real budget and executed value. The result would be something like:

 INIT    REAL  Dif%  EXEC  Dif%

$1000  $900  -10%  $1100 +10%

 Is there a way to do it with custom calculated fields?

Thanks a lot!