Differences between last 5 months

Hi @Theriaux ,

I created a sample pbix file(see attachment) for you, please check whether that is what you want. You can create a measure as below:

Difference = 
VAR _seldate =
    SELECTEDVALUE ( 'Table'[Date] )
VAR _enddate =
    EOMONTH ( EDATE ( _seldate, -1 ), 0 )
VAR _startdate =
    EDATE ( _enddate, -5 ) + 1
VAR _pre5years =
    SUMX (
        FILTER (
            ALLSELECTED ( 'Table' ),
            'Table'[Date] >= _startdate
                && 'Table'[Date] <= _enddate
        ),
        [Total cases]
    )
RETURN
    IF ( ISBLANK ( _pre5years ), BLANK (), [Total cases] - _pre5years )

You can refer the following links to get the values for last N months:

Display Last N months data in Power BI

Display Last N Months & Selected Month using Single Date Dimension in Power BI

If the above one can't help you get the desired result, please provide some sample data in your tables (exclude sensitive data) with Text format and your expected result with backend logic and special examples. It is better if you can share a simplified pbix file. You can refer the following link to upload the file to the community. Thank you.

How to upload PBI in Community

Best Regards