You can create a calculated field in the pivot table --

Select a cell in the pivot table
On the PivotTable toolbar, choose PivotTableFormulasCalculated Field
Type a name for the field, and in the Formula box, enter a formula to
calculate the commission.

FARAZ QURESHI wrote:
Can one create a custom field in mid of a pivot table. For instance:

1. Original PIVOT TABLE
Sales Zone 1 Sales Zone 2 Sales Zone 3 Total

2. Custom PIVOT TABLE
Sales Zone 1 Sales Zone 2 (Net of Commission in Zone 2) Sales Zone 3 Total




--
Debra Dalgleish
Contextures
http://www.contextures.com/tiptech.html