iReports Custom Fields for columns (sum, average, etc)
Right-Click on Variables and click Create Variable
Click on the new variable
a. Notice the properties on the right
Rename the variable accordingly
Change the Value Class Name to the correct Data Type
a. You can search by clicking the 3 dots
Select the correct type of calculation
Change the Expression
a. Click the little icon
b. Select the column you are looking to do the calculation for
c. Click finish
Set Initial Value Expression to 0
Set the increment type to none
Set the Reset Type (usually report)
Drag a new Text Field to stage (Usually in Last Page Footer, or Column Footer)
Select the new variable
Click finish