Cumulative run rate calculation

Hi Cmoore 

You can create a new column with the following DAX instead of using Power Query. Ensure that Month Year column is of Date data type. Demo pbix has been attached at bottom. 

Run Rate Cumulative = 
VAR lastActualMonth =
    MAXX (
        FILTER ( 'Table', 'Table'[TY Actual Cumulative] <> BLANK () ),
        'Table'[Month Year]
    )
RETURN
    SUMX (
        FILTER ( 'Table', 'Table'[Month Year] <= EARLIER ( 'Table'[Month Year] ) ),
        'Table'[Input Value TY]
    )
        + IF (
            ISBLANK ( 'Table'[Input Value TY] ),
            SUMX (
                FILTER (
                    'Table',
                    'Table'[Month Year] > lastActualMonth
                        && 'Table'[Month Year] <= EARLIER ( 'Table'[Month Year] )
                ),
                'Table'[Avg. Monthly Run Rate]
            )
        )

Best Regards,
Community Support Team _ Jing
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