i've created a pivot table from data i have; i would like to add up cells from two columns and the sum to be in a third column. However, since the PT has a lot of grouping done; if i play with the table, the column where i manually inserted the sum is still. (this is a simplified example)

Example:
Column A ------ Column B ------ Column C ------- SumColB+ColC (Manual)
1 John 14,500 9,000 +B1+C1
2 Tailor 13,500 8,000 +B2+C2
3 Mich 12,500 7,000 +B3+C3
4 Ban 11,500 6,000 +B3+C3

If i filter the data to show sub categories; i.e.
Column A ------ Column B ------ Column C ------- SumColB+ColC (Manual)
1 John 14,500 9,000 +B1+C1
JDO1 55 60 +B2+C2
2 Tailor 13,500 8,000 +B3+C3
3 Mich 12,500 7,000 +B3+C3
TT2 1110000
4 Ban 11,500 6,000

The manual column i created to sum up the cells remain stationary and does not follow the cells they are meant to sum.

Help?