How to do Demand Planning & stock forecast ?

Excel does math so what you have to do is to decide what calculations have to be made. For example, you have sales data for various SKUs. By listing the SKU sales by dates, you can see what the trend is. You can then take the average increase or decrease (math) and add or subtract that from the latest sales (math again) to get an estimate of future sales.

Seeing that you warehouse product, you can take advantage of the best bulk prices if the warehousing costs are less than the sales savings (math again). Is your expected demand large enough to qualify and make worth while bulk purchases at off season rates?

Now knowing what you have to calculate, you can layout your Excel worksheet so that you can make the calculations which will mostly be adding (SUM function or just +), subtraction (-), division (/), multiplication (*) and AVERAGE.

The enclosed workbook is just an idea on how to setup in order to make the calculations that you may have to make. It has 1 row per SKU and 1 column per year for various data items. Try and create the worksheet that works for you. If you run into difficulty, post the problem that you are facing and we can try and help you solve it.