dax

Hi Anonymous ,

I suggest you to create a "DimDate" table to help calculation.

DimDate = 
VAR _CALENDAR =
    CALENDARAUTO()
RETURN
    ADDCOLUMNS (
        _CALENDAR,
        "Year", YEAR ( [Date] ),
        "Month", MONTH ( [Date] ),
        "MonthName", FORMAT ( [Date], "MMMM" ),
        "RANKX",
            RANKX ( _CALENDAR, YEAR ( [Date] ) * 100 + MONTH ( [Date] ),, ASC, DENSE )
    )

Measure:

Sum 3 month count = 
VAR _SUMMARIZE =
    SUMMARIZE (
        ALL ( DimDate ),
        DimDate[Year],
        DimDate[MonthName],
        DimDate[RANKX],
        "P1M", [p1m]
    )
RETURN
    SUMX (
        FILTER (
            _SUMMARIZE,
            [RANKX]
                > MAX ( DimDate[RANKX] ) - 3
                && [RANKX] <= MAX ( DimDate[RANKX] )
        ),
        [P1M]
    )

Result is as below.

Best Regards,
Rico Zhou

If this post helps, then please consider Accept it as the solution to help the other members find it more quickly.