Advice needed to speed this code.

[snb]

In that case; if you want to sum left of cell in column5:

Sub M_snb()
  sn = Cells(1).CurrentRegion
  
  For j = 2 To UBound(sn)
     sn(j, 5) = Evaluate(Split(Join(Application.Index(sn, j), "+"), "+" & sn(j, 5))(0))
  Next
End Sub