Subtract columns

[Anonymous]

Hello,

My end goal is to make an automated reporting procedure, where I will copy/paste every month a new excel file (trial balance of each month) on a folder and then the outcome will appear on a Power BI dashboard in a matrix format where each column is a month and other columns are Q1,Q2,6-month, etc. Each row represents balance sheet's account numbers. The original files have >100k rows/accounts and the date is in a format D/M/YYYY.

My problem is that the trial balance has cummulative numbers, so I have to substract each column to have the outcome for a specific month i.e. Mar - Feb = Change in March. Any idea on how can I tackle this problem?

Unfortunatelly, I cannot share my original data so I created the power query table and the reporting matrix on the dashboard with dummy numbers.

Thanks in advance! 

Cheers,

Alex