How do I Add new formula columns in Pivot Table

[Financialrep]

Hi. How do I insert additional formula based columns that would calculate monthly/period variance from Target and YTD target variance from total months/periods?

 

[Financialrep]

[TABLE="width: 640"]
<tbody>[TR]
[TD]Department[/TD]
[TD]PP-1[/TD]
[TD]PP-2[/TD]
[TD]Month Target[/TD]
[TD]Variance[/TD]
[TD] YTD Target[/TD]
[TD] Total Variance[/TD]
[/TR]
[TR]
[TD]A[/TD]
[TD] 3 [/TD]
[TD] 6 [/TD]
[TD="align: right"]1[/TD]
[TD="align: right"](5)[/TD]
[TD="align: right"]2[/TD]
[TD="align: right"](7)[/TD]
[/TR]
[TR]
[TD]B[/TD]
[TD] 25 [/TD]
[TD] 14 [/TD]
[TD="align: right"]9[/TD]
[TD="align: right"](13)[/TD]
[TD="align: right"]18[/TD]
[TD="align: right"](21)[/TD]
[/TR]
[TR]
[TD]C[/TD]
[TD] 8 [/TD]
[TD] 18 [/TD]
[TD="align: right"]16[/TD]
[TD="align: right"](17)[/TD]
[TD="align: right"]32[/TD]
[TD="align: right"]6 [/TD]
[/TR]
[TR]
[TD]D[/TD]
[TD] 6 [/TD]
[TD] 1 [/TD]
[TD="align: right"]7[/TD]
[TD="align: right"]0 [/TD]
[TD="align: right"]14[/TD]
[TD="align: right"]7 [/TD]
[/TR]
[TR]
[TD]F[/TD]
[TD] 14 [/TD]
[TD] 14 [/TD]
[TD="align: right"]8[/TD]
[TD="align: right"](13)[/TD]
[TD="align: right"]16[/TD]
[TD="align: right"](12)[/TD]
[/TR]
[TR]
[TD]G[/TD]
[TD] 1 [/TD]
[TD] 8 [/TD]
[TD="align: right"]12[/TD]
[TD="align: right"](7)[/TD]
[TD="align: right"]24[/TD]
[TD="align: right"]15 [/TD]
[/TR]
[TR]
[TD]H[/TD]
[TD][/TD]
[TD] 4 [/TD]
[TD="align: right"]0[/TD]
[TD="align: right"](3)[/TD]
[TD="align: right"]0[/TD]
[TD="align: right"](4)[/TD]
[/TR]
[TR]
[TD] Total[/TD]
[TD] 57[/TD]
[TD] 65[/TD]
[TD] 53 [/TD]
[TD="align: right"](58)[/TD]
[TD] 106 [/TD]
[TD] (16)[/TD]
[/TR]
</tbody><colgroup><col><col><col><col><col span="3"></colgroup>[/TABLE]