You can either stick with his default assumptions about future market performance or change these to reflect your own beliefs. Next, you'll need to enter your annual portfolio expense ratio in cell B18. The target final value shown in cell B37 is where you'd like to model your portfolio ending at the end of your retirement as a percentage of your starting value. Finally, let's ignore the cape model in cell B38 for now. This is an optional element but one that I think is really interesting. We'll come back to this in part two of this series.