Sub CutBeforeSubstring()

Dim dblPosition, dblSubLength, dblTotalLength As Double
Dim strToFind, strLookIn, strResult As String

'Record the value in the active cell.
strLookIn = ActiveCell.Value

'Get the string to search for and determine its length.
strToFind = InputBox("Keep after which substring?")
dblTotalLength = Len(strLookIn)
dblSubLength = Len(strToFind)

'Find the string within the cell.
dblPosition = Application.WorksheetFunction.Find(strToFind, strLookIn)

'Assign the characters up to the break to a new string.
strResult = Right(strLookIn, dblTotalLength-dblPosition-dblSubLength+1)

'Assign the string to the active cell.
ActiveCell.Value = strResult

End Sub