Power Query - Nested loop iteration with the output in the first row and so on

Hi Anonymous 

Do you must do it with Power Query? If you may accept DAX solutions, you can try my method below. If you want to do it only with Power Query, let me know then I will try to work it out. 

First add a custom column with Power Query to get Month Start Date for every row. 

Date.FromText("1"&[Month])

After applying the change to data model, create calculated columns with the following DAX formula. 

Month WIP used in = 
VAR __table =
    SELECTCOLUMNS (
        FILTER ( 'Table', 'Table'[YearMonth] <= EARLIER ( 'Table'[YearMonth] ) ),
        "_yearMonth", 'Table'[YearMonth],
        "_WIP", 'Table'[WIP],
        "_fees", 'Table'[Fees]
    )
VAR __firstWIP = 'Table'[WIP]
VAR __table2 =
    ADDCOLUMNS (
        __table,
        "_runningWIP",
            __firstWIP
                - SUMX ( FILTER ( __table, [_yearMonth] >= EARLIER ( [_yearMonth] ) ), [_fees] )
    )
RETURN
    MAXX ( FILTER ( __table2, [_runningWIP] <= 0 ), [_yearMonth] )

# of months = DATEDIFF ( 'Table'[Month WIP used in], 'Table'[YearMonth], MONTH ) + 1

Running WIP = 
'Table'[WIP]
    - SUMX (
        FILTER (
            'Table',
            'Table'[YearMonth] <= EARLIER ( 'Table'[YearMonth] )
                && 'Table'[YearMonth] >= EARLIER ( 'Table'[Month WIP used in] )
        ),
        'Table'[Fees]
    )

Best Regards,
Community Support Team _ Jing
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