Rolling3months

Hello wyanjaspew 

I would first create one 'DateTable', properly mark it as a Date table in Power BI and use it to filter the fact table by 'one to many' relationship. You can either create Date table in Power Query or with DAX in Power BI. Below is the one with DAX. 

DateTable = 
ADDCOLUMNS(
    CALENDAR(
        DATE(2025,1,1),
        DATE(2025,12,31)
    ),
    "Year", YEAR([Date]),
    "Month", MONTH([Date]),
    "MonthName", FORMAT([Date], "MMMM"),
    "Quarter", "Q" & QUARTER([Date]),
    "YearMonth", FORMAT([Date], "yyyy-MM")
)

After this, use below Measure for 'Rolling_3_Month' calculation (assuming your Total Service ID = DISTINCTCOUNT(test[ServiceID]) ) 

Rolling_3_Months = 
VAR _currentDate = MAX(DateTable[Date])
VAR _rollingPeriod = 
    DATESINPERIOD(
        DateTable[Date],
        _currentDate,
        -3,
        MONTH
    )
VAR _result=
        CALCULATE(
            AVERAGEX(
                VALUES(DateTable[MonthName]), 
                [Total Service ID]
            ),
            _rollingPeriod
        )

RETURN
    IF(
        ISBLANK([Total Service ID]),
        BLANK(),
        _result
        )

With small portion of sample data 

Hope this helps:)