<![CDATA[The inventory control system at ISP company has not been optimally implemented, resulting in frequent stock-outs, high emergency purchasing frequency, and increased inventory costs due to the absence of a systematic approach for determining inventory requirements, optimal order quantities, and reorder timing. This study aims to identify the root causes of stock-outs using Root Cause Analysis (RCA), forecast inventory demand using the Trend Projection method, determine the optimal order quantity using Part Period Balancing (PPB), and establish the appropriate Reorder Point using the Reorder Point (ROP) method. This research employed a quantitative descriptive approach using inventory, demand, and purchasing data from January to December 2025 for seven fast-moving inventory items, namely ONT, Pathcore, Cable Clamps, Connector Pins, Adhesive Tape, Adapters, and Fiber Optic Cables. The results indicate that the primary causes of stock-outs are related to human factors, methods, materials, and the working environment. The Trend Projection method successfully generated demand forecasts that can serve as the basis for future inventory planning. The implementation of the PPB method produced more optimal order quantities by balancing ordering and holding costs, while the ROP method determined appropriate Reorder Points to ensure replenishment before inventory reached critical levels. Therefore, the integration of RCA, Trend Projection, PPB, and ROP proved effective in improving inventory control, reducing the risk of stock-outs, minimizing inventory costs, and supporting warehouse operational efficiency at PT AST.]]>
