Using VBA to apply Conditional Formatting based on a calculation to Column

Hi I have been looking through posts to find the answer but I am getting more confused. Hopefully some kind person can show me the code...

I have 3 columns of numeric data in my spreadsheet that has been populated by a 3rd party import application (I cant access the spreadsheet until after it is populated from this application which removes all conditional formatting but does keep any VBA code etc). The 3 columns are fixed position but there are hundreds of rows (possibly a different number of rows each time the import is run)

I need to see if Column 1 + Column 2 <> Column 3. If so then I need column 3 to be highlighted (lets say in red background).

I would be very grateful if someone could provide me with the code to apply the formatting. I would launch it from a command button.

Thank you so much.

Tony

Hi Tony..
Try this code & a workbook is attached for you to play with.
I think it does what you're after.

Option Explicit

Sub SumFormat()

    Application.ScreenUpdating = False
    
    Dim Wsht1 As Worksheet ' Worksheet 1
    Dim Col3Range As Range ' Column C
    Dim Col1Cell As Range
    Dim Col2Cell As Range
    Dim Col3Cell As Range
    Dim TopRow As Long ' Top row number where data starts
    
    TopRow = 1
    Set Wsht1 = ThisWorkbook.Sheets(1)
    Set Col3Range = Wsht1.Range(Wsht1.Cells(TopRow, 3), Wsht1.Cells(Rows.Count, 3).End(xlUp))
    Set Col1Cell = Wsht1.Cells(TopRow, 1) ' A1
    Set Col2Cell = Wsht1.Cells(TopRow, 2) ' B1
    Set Col3Cell = Wsht1.Cells(TopRow, 3) ' C1
    Col3Range.ClearFormats ' Clear any previous formatting
        
        
    For Each Col3Cell In Col3Range
        If Col1Cell.Value + Col2Cell.Value <> Col3Cell.Value Then ' Condition is met
            With Col3Cell
                .Interior.Color = RGB(218, 150, 150) ' Light Red
                .BorderAround LineStyle:=xlContinuous, Weight:=xlThin, Color:=RGB(255, 0, 0) ' Red Border
            End With
'   Move down a row
                TopRow = TopRow + 1
                Set Col1Cell = Wsht1.Cells(TopRow, 1)
                Set Col2Cell = Wsht1.Cells(TopRow, 2)
            Else ' If the condition wasn't met
'   Move down a row
                TopRow = TopRow + 1
                Set Col1Cell = Wsht1.Cells(TopRow, 1)
                Set Col2Cell = Wsht1.Cells(TopRow, 2)
            End If
    Next Col3Cell
    
    Application.ScreenUpdating = True
    
End

End Sub

Try this. I've changed it to a worksheet change event for any of the cells in the range A1:C? (bottom row on column C) & on workbook open it triggers the same macro. If you don't need the workbook open option, comment out or delete the code in the Workbook module. Hopefully that covers all bases
Cheers

Many thanks. I am out tonight so will use tomorrow. Many thanks for all your help. Tony

All sorted. Many thanks Tony

No Problem