Days inventory outstanding (DIO) measures the average number of days it takes a business to sell its inventory. DIO = 365 / inventory turnover. It is a component of the cash conversion cycle.
DIO quantifies how long inventory sits before being sold. Low DIO = inventory moves quickly (efficient operations, strong demand). High DIO = inventory ties up capital for longer (slow-moving goods, overstocking, or demand weakness). DIO is calculated as: (Average Inventory / COGS) × 365. Or equivalently, 365 / Inventory Turnover Ratio. 'Average inventory' uses the mean of beginning and ending inventory balances for the period. DIO is one component of the cash conversion cycle (CCC): CCC = DIO + DSO − DPO. DIO adds to the cycle (cash is tied up in inventory). DSO (days sales outstanding — receivables collection) also adds. DPO (days payable outstanding — how long you take to pay suppliers) subtracts (you're using supplier credit to fund the cycle). A short CCC means the business cycles cash quickly; a long CCC requires more working capital financing. Industry benchmarks vary enormously. Grocery retail: 10–20 days. Apparel retail: 60–120 days. Auto dealers: 45–75 days. Aircraft parts distributors: 180+ days. Compare DIO against industry norms — both extremes signal potential issues. Very low DIO may indicate stockout risk (losing sales due to insufficient inventory). Very high DIO may indicate overbuying or demand problems.
Asset-based lenders and inventory lenders use DIO to assess how quickly they could liquidate the inventory if needed and how much working capital the inventory cycle consumes. High DIO relative to industry norms raises questions about demand, obsolescence, and liquidation risk. It also affects working capital line sizing — businesses with longer DIO need more facility size to cover the same revenue volume.
Overbuying (purchasing more than demand justifies), slow-moving SKUs, seasonal inventory building (intentional), demand decline, supply chain disruptions causing forward purchasing, or product quality issues leading to returns and holds. Rising DIO quarter over quarter without a clear strategic reason is a warning signal for lenders and operators.
Not necessarily. Extremely low DIO may indicate stockout risk — you're selling faster than you can replenish, potentially losing sales. It may also indicate under-investment in safety stock, leaving the business vulnerable to supply disruptions. The optimal DIO balances working capital efficiency (lower is better) against service level and supply chain resilience.