Gross Profit- Power Pivot

I have multiple tables linked and generating a basic pivot P&L showing revenue, cost of sales, other expenses. 1 table (transactions) contains all of the revenue and expense transactions along with an associated account index. This table is linked to a Chart table holding the index and associated account number as well as roll up grouping (revenue, cost of sales, other expenses, etc...) for a given account number. What I'm attempting to do is have the pivot calculate a gross margin by netting the revenue and cost of sales roll up grouping totals. Multiple searches have left me wondering if I have to use some form of DAX to create. Is there a much simpler way to do this?

Created additional grouping for revenue and cost of goods sold accounts with the label "Gross Margin". Then labled other expenses and revenues as such. Primary row gouping now uses this grouping to get a nice gross marging subtotal.