How to Subtract value of current month from previous month
Hey there! There are a few different ways to achieve this, but generally grouping by month, adding an aggregation Sum([Revenue]) for example, then using the Lead() function to get the previous row is the way to handle this. We have a write up here on a similar period over period analysis.
You could also perform a lookup using a negative DateAdd, though this is more time consuming and reserved for more complicated analysis.
From here, you can perform the simple subtraction as you need.