Creating an Insurance Loss Triangle

[Dneal850]

I am trying to create a loss/claim triangle where I have loss values or claim counts for each month and would like to show how the losses progress throughout the year. I have tried several other solutions posted on here but haven't had any luck. 

I have loss data by month and year that gets updated every month and would like the triangle to do so as well. They are simple to make in excel but have been causing me problems in BI. Any tips/solutions would be appreciated. I'm attaching an screenshot of what I would like to produce in BI. I would also like to do this with loss amounts, not just claim counts. 

[Fowmy]

@Dneal850 

Can you share a sample Excel file with the above calculation as shown? . You can save your Excel file in One Drive or Google Drive then share the link here.