I have a pivot table showing revenue grouped by month in each row (among other things).

I've added an aggregate running total as a column which adds up the revenue for each month and shows the running sum.

However when I change the order of the date column so that the latest date is at the top, and the oldest date is at the bottom, the running sum still calculates from the top of the table to the bottom.. which means the latest month shows 0 and it accumulates down to the oldest date which shows the running total at the bottom.

How can I get it to show the running sum going up the table?