Calculate previous month's total

Hi,

I am looking to return a previous month's total in my matrices. I've looked at parallelperiod but I either don't understand the function, or it's not working in my particular setup.

I have a query with all of my data - e.g. date of trade (may be multiple trades on a date) and size of each trade in another column

I then have another query with a range of dates covering several years and various different breakdowns of the date - month name, day name, financial year month name (months ordered by financial year - i.e. July is 1 instead of 7), quarter (labelled Qtr 1, etc), etc. I have the trade date in my source data linked to the date in this query.

In my output matrices in Power Bi I use fields from the date query to summarise data. E.g. the rows of my table are Financial Month Name from the date query. I have a query that sums the trade size column and is the values in this matrix. I'm looking to build a measure that allows me to display the previous month's total trade size against a particular month.

I tried using Parallel Period as follows: Total Volume M-1 = CALCULATE(SUM('Trade Data'[Volume]),DATEADD('Date Lookup'[Trade Date].[Date],-1,month)) but when I use Financial Month Name (a column in my Date Lookup table) it just repeats the same data in the Total Volume and Total Volume M-1 column.

Can anyone suggest a function to achieve this, or explain how I'm using Parallel Period incorrectly?

Thanks