Variance Calculation on the same column (Sum)

[st7979]

Hi experts:

I have a report that needs to calculate variance.

i.e Jan Feb Mar Apr...
2014 1 10 30 20
2015 0 20 50 5
Variance 1 -10 -20 15

How can we subtract the sum from the same row? I know I can manually create running total and evaluate the formula as month = Jan, month = Feb and split them from 2014, 2015 but if I need this report run next year, then I will need to write more running total.

Thanks