A 5-Step Process to Forecasting Sales
For the following year, if everything remains the same, sales generated will equal $16,120 (114 * 0.40 * $200 + 70 * $100 = $16,120).
Simply replicate this process for three more years, and you have your forecast for 2015.
The beauty of this process is that you can change new customer assumptions, customer retention assumptions and/or spend per customer assumptions to see what impact the assumptions have on the future of your business. You can identify a path that leads you to the sales figures that management is looking for.