The article discusses the methodology for calculating the turnover coefficient and period of turnover of inventory for a company with irregular stock on hand. It emphasizes the importance of the indicator characterizing the turnover of working capital associated with inventory. A scientific and methodological approach is proposed for evaluating the product turnover period to optimize and enhance the efficiency of managing an e-commerce business. The article identifies the problems that arise when using the classical method for calculating the turnover coefficient and turnover period of goods and demonstrates the challenges of automatically calculating these indicators using alternative calculation schemes proposed by Ukrainian and foreign authors. A new algorithm for calculating the turnover period of goods based on an “event-based” approach is proposed. This methodology involves capturing the timing of “events” such as the purchase and sale of goods, which represent moments when funds are tied up in inventory and then returned to circulation. Model examples illustrate the accurate calculation of the turnover period for irregular goods that may temporarily be absent from a company’s inventory. The ability to automatically calculate these indicators for a significant number of product items is also demonstrated. The methodology proposed by the authors is universal and does not require additional conditions when calculating turnover indicators, whether for regularly stocked items, periodically stocked items, or seasonally stocked items. The methodology is not limited by the calculation period and can be equally effective for short and long calculation periods. Automating the calculation of inventory turnover based on the proposed “event-based” algorithm significantly enhances the efficiency of managing e-commerce businesses and improves the methodology of ABC analysis of a company’s product portfolio. The authors’ methodology for calculating the turnover period of goods is original, with no similar methods found in other publications related to the turnover of working capital associated with a company’s inventory.