Indonesia's vast archipelago presents logistical challenges for businesses, leading many to adopt decentralized inventory systems. However, this approach can result in inventory imbalances and stagnation, emphasizing the need for effective supply chain management and demand forecasting. A case study of PT Mandala Persada, a nationwide spare parts distributor, reveals a significantly lower inventory turnover ratio (ITR) compared to competitors, stemming from inaccurate demand planning. This study aims to identify the root causes of forecasting inaccuracies and inventory inefficiencies at PT Mandala Persada, develop targeted interventions to improve forecast accuracy and optimize stock levels, and evaluate the impact of these improvements on the ITR, providing practical recommendations for inventory management in complex environments like Indonesia. The research focuses on PT Mandala Persada's ITR and historical data from 2024, exploring the problem, theoretical foundations, research methodology, data analysis, and proposed business solutions.