Loop for vba macro from a specific column to the last column with data

OK, give this a try

Sub x()

Dim r As Long, c As Long, rData As Range, i

Const n As Long = 160

Sheet2.Activate

Set rData = Range("A1").CurrentRegion

For r = 2 To rData.Rows.Count
    i = Application.Match(CLng(DateSerial(Year(Cells(r, 2)), Month(Cells(r, 2)), 1)), rData.Rows(1), 0)
    If IsNumeric(i) Then
        c = 1
        Do While WorksheetFunction.Sum(Cells(r, i).Resize(, c)) < Cells(r, 1)
            If Cells(r, 1) - WorksheetFunction.Sum(Cells(r, i).Resize(, c)) < n Then
                Cells(r, i - 1 + c) = Cells(r, 1) - WorksheetFunction.Sum(Cells(r, i).Resize(, c))
            Else
                Cells(r, i - 1 + c) = n
            End If
            c = c + 1
        Loop
    End If
Next r

With rData
    .Offset(1, 3).Resize(.Rows.Count - 1, .Columns.Count - 3).SpecialCells(xlCellTypeBlanks).Value = 0
End With

End Sub