This paper develops a demand forecasting model based on SARIMA and inventory management methodologies such as 5S, FIFO and ABC Classification in a food, beverage and cleaning products marketing company. The integration of these tools allowed to improve the accuracy of the forecasts, optimize inventory turnover and reduce the obsolescence rate, contributing significantly to the increase in sales conversion and customer satisfaction. By using the SARIMA model, replenishment decisions were adjusted to seasonal patterns, while 5S and FIFO methodologies improved warehouse organization and inventory traceability. The results of the project show a positive impact on key indicators such as MAPE, RMSE and MAE, as well as on the customer conversion rate, achieving an increase from 78% to 95%. In addition, training processes and audits were implemented to ensure the sustainability of improvements in the long term. This approach demonstrates how the integration of mathematical models and lean manufacturing practices can transform operational efficiency in the retail sector.