Looping Excel Formulas

this should work for you

Sub LoopInOut()
    i = 3
    With Sheets("To Plot")
        .Range("A" & i).Value = .Range("E5").Value
        Do Until .Range("A" & i - 1).Value >= .Range("F5").Value And i > 3
            If i > 3 Then .Range("A" & i).Value = Round(.Range("A" & i - 1).Value + .Range("G5").Value, 4)
            Sheets("GUI").Range("C10").Value = .Cells(i, 1).Value
            Application.Calculate
            .Cells(i, 2).Value = Sheets("GUI").Range("C15").Value
            .Cells(i, 3).Value = Sheets("GUI").Range("C14").Value
            i = i + 1
        Loop
    End With
End Sub