I would like to have a pivot table calculate the difference between columns in the table but I don't see how to do that.

My data is rows of expenses by month by expense category, for example

Category, Month, Amount

Power, January 2018, $115

Water, January 2018, $25

Power, February 2018, $120

Water, February 2018, $22

My pivot table has 

Category as the rows

Month as the columns

Amount as the data in each column

For example

	January 2018	February 2018
Power	$115	$120
Water	$25	$22

Is there a way that I could have it calculate the month to month difference?  I know it will sum the row for me and give me a grand total, but I want to have the difference between each column.

Thanks in advance.