What I’m attempting to do:

Loop through 2 worksheets (same workbook), comparing 2 criteria (farm and batch). If criteria match, then sum the values in the ‘No. of Samples” cells and paste to “Total Samples”

What actually happens:

When both criteria are met, the first 2 rows of values are summed and pasted to the correct cell. But only the first 2 rows. So the Do While is not… doing while. Or else it has reason to skip cells or exit the loop early. I suspect I have too many iterations going on. And Do Loops can easily devolve into infinite loops, as I have found out.

Also, my immediate window shows the first iteration in row 1815 and not 3. (s = row# in Source page)

New Sum: 190

s, Num Samples: 1815, 95 

I’m not sure exactly where to go from here, any insight would be appreciated.

Sub ProjectDataCalcs()

Dim Src As Worksheet: Set Src = Sheets("Plate Analysis")
Dim Dest As Worksheet: Set Dest = Sheets("Project Analysis")

Dim Sum As Long
Sum = 0
Dim s As Long, d As Long, LR As long, LR2 As Long

LR = Dest.Cells.Find("*", SearchOrder:=xlByRows, SearchDirection:=xlPrevious).Row
LR2 = Src.Cells.Find("*", SearchOrder:=xlByRows, SearchDirection:=xlPrevious).Row

    ' effectively a SUMIFS loop
        For s = 3 To LR2
        Sum = Src.Cells(s, "D").Value ' Number of Samples per Plate
        Debug.Print "s, Num Samples: " & s & ", " & (Sum)
         For d = 3 To LR
        'while batch = batch and farm = farm,
        'sum cell value (not add row count) number of samples per plate
         Do While Src.Cells(s, "H").Value = Dest.Cells(d, "E").Value And _
         Src.Cells(s, "I").Value = Dest.Cells(d, "D")

            'Add value in cell to existing value;
            'add Number of Samples in line to running total of samples
            Sum = Sum + Src.Cells(s, "D").Value

            Debug.Print "New Sum: " & (Sum)
            'Sum to Total Samples cell in col L
            Dest.Cells(d, "L").Value = Sum
            Exit Do
          Loop
         Next d
        Next s

End Sub