Estimated Delivery date based on cumulative count

learner03 Great to hear. If you need them, I revised the FIFO, LIFO and optimized columns and measures into FIFO 2, LIFO 2, etc. so you have 4 different ways of fulfilling backlog as both columns and measures without having to use GENERATESERIES. Attached PBIX.

Greg_Deckler That's Brilliant !! Thanks again

Greg_Deckler an extention to the report, how can I get the column next to the the new estimated delivery date where it can tell which associated Document number is used for the fulfilment of quantiy.

example-

In Backorder Table- the first few row are fulfilled by the first line of Open Puchase table. So, the associated Document number will be 229160 all the way through where 11/02/2022 and 230426 where 15/04 is in esti delivery column.

In Open Purchase table-

learner03 Two ways based on the latest code from email. This version returns the last purchase order used to fulfill the backorder:

Purchase Orders Used = 
    VAR __DaysToFulfill = 10
    VAR __ItemCode = [Item Code]
    VAR __Simba = [Simba Ref#]
    VAR __Date = [Date]
    VAR __QtyToFulfill = 
        SUMX(
            FILTER(
                'Backorders',
                [Item Code] = __ItemCode && 
                VALUE( TRUNC([Date]) & "." & RIGHT([Simba Ref#],LEN([Simba Ref#])-2)) <= VALUE( TRUNC(__Date) & "." & RIGHT(__Simba,LEN(__Simba)-2))
            ),
            [Backorder Qty]
        )
    VAR __Table = FILTER('On Purchase',[Item Code] = __ItemCode)
    VAR __Table1 = 
        ADDCOLUMNS(
            ADDCOLUMNS(__Table,"__tqty",SUMX(FILTER(__Table,[ETA W/H] <= EARLIER([ETA W/H])),[Qty Balance])),
            "__LoopCounter",[__tqty] - __QtyToFulfill
        )
    VAR __TargetDate = MINX(FILTER(__Table1, [__LoopCounter] >= 0),[ETA W/H])
    VAR __FulfillmentDate = IF(__TargetDate = BLANK(),BLANK(),__TargetDate+__DaysToFulfill) 
RETURN
    MAXX(FILTER(__Table1,[ETA W/H] = __TargetDate),[Document Number])

Here is one that preserves history so to speak:

Purchase Orders Used 2 = 
    VAR __DaysToFulfill = 10
    VAR __ItemCode = [Item Code]
    VAR __Simba = [Simba Ref#]
    VAR __Date = [Date]
    VAR __QtyToFulfill = 
        SUMX(
            FILTER(
                'Backorders',
                [Item Code] = __ItemCode && 
                VALUE( TRUNC([Date]) & "." & RIGHT([Simba Ref#],LEN([Simba Ref#])-2)) <= VALUE( TRUNC(__Date) & "." & RIGHT(__Simba,LEN(__Simba)-2))
            ),
            [Backorder Qty]
        )
    VAR __Table = FILTER('On Purchase',[Item Code] = __ItemCode)
    VAR __Table1 = 
        ADDCOLUMNS(
            ADDCOLUMNS(__Table,"__tqty",SUMX(FILTER(__Table,[ETA W/H] <= EARLIER([ETA W/H])),[Qty Balance])),
            "__LoopCounter",[__tqty] - __QtyToFulfill
        )
    VAR __TargetDate = MINX(FILTER(__Table1, [__LoopCounter] >= 0),[ETA W/H])
    VAR __FulfillmentDate = IF(__TargetDate = BLANK(),BLANK(),__TargetDate+__DaysToFulfill) 
RETURN
    CONCATENATEX(FILTER(__Table1,[ETA W/H] <= __TargetDate),[Document Number],", ")