The planner has an additional inputs section. Here you can factor in expenses such as college costs for your children. It also allows you to include any additional income that may come in only occasionally. With this, you can set the specific years the income may come in to get a more accurate result.
Additionally, you can set portfolio return for specific years. That way if you plan to be more aggressive with your investments when younger but less aggressive as you get older, you can again plan more accurately.