IntroductionBased on the principle that this model is easy and intuitive to apply in practice to forecast MAD Ltd's C1 product, especially providing information to people who they do not have any VBA skills and forecasting knowledge. This model uses solver, Holt-Winters forecasting method and VBA to automatically get the calculation to get the forecast result of next quarter or whole year. This report will first provide guidance on how to use this model and its accuracy. It then illustrates what forecasting, computer programming, and VBA are and how these theories apply to this model. Finally, indicated the process of maintaining this model and the limitations of this model if the user wants to conduct further processes. Help this forecasting model. To get the next quarter's accurate C1 product amount, the manager needs to enter the current quarter's observation data of C1. amount first by clicking down at the front of Excel. Then it will ask the user to enter the data of the current quarter's sales amount. Tap the actual number of the current quarter's sales amount, then Excel will ask the user to make sure the recorded data is correct, if it is not correct, the template will exist automatically, the user need to press the bottom again to enter the data correct. If the data entered is correct, Excel will show an output box of results due to Excel running the solver down to the minimum prediction error error. Finally, Excel will display a Product C1 message box of next quarter's forecast amount and total cost forecast. Since the data is updated quarterly, updating the current quarter's unit sales will improve the accuracy of forecasting the next quarter's unit sales. This model assumes that MAD Ltd predicts who... halfway down the sheet of paper... very simplified and automatic. Depending on the setting, it is suitable for MAD Ltd company for long-term operation without complicated input steps and frequent maintenance tasks. However, some disadvantages still exist. Since this model mainly provides figures, difficult to compare and illustrate errors between actual observation, quarterly forecasts and annual forecasts. Therefore, using line graph could clearly illustrate the trend and differences between these variables. The user needs to edit the line chart data provided in the Excel file. According to the situation of the C1 product of MAD Ltd company, design this forecasting process to get optimized results to predict the C1 product aimed at people of different backgrounds. For future work, this model could also apply to other products that exhibit trends and seasonality, to improve their accuracy and reduce operational costs.