DIO
Days Inventory Outstanding (DIO) is the average number of days a company holds inventory before selling it. It is the inventory component of the Cash Conversion Cycle and a key indicator of supply chain and demand planning efficiency.
Inventory is dead capital until it sells. Every day a company holds raw materials, work-in-progress, or finished goods on the shelf is a day of capital tied up, warehousing cost incurred, and obsolescence risk accruing. Days Inventory Outstanding turns this into a single comparable metric. For manufacturing, distribution, and retail businesses, DIO is one of the most operationally controllable working capital levers and a direct measure of how well demand planning matches supply.
The standard formula is:
DIO = (Average Inventory / Cost of Goods Sold) x Number of Days
Average inventory is typically calculated as (Beginning Inventory + Ending Inventory) / 2 for the period. COGS is from the same period. Number of days is 365 for annual analysis, 90 for quarterly.
A worked example: a distributor holds 12 million euros average inventory and has 60 million euros annual COGS. DIO = (12,000,000 / 60,000,000) x 365 = 73 days. The distributor holds about 2.5 months of inventory on average.
Some companies use Ending Inventory rather than Average Inventory for a current snapshot; the Average Inventory method is more reliable for trend analysis because it smooths quarter-end inventory builds.
Benchmarks vary dramatically by industry because business models differ in how inventory flows:
Trend matters more than absolute level. A manufacturer at 120 days DIO improving to 100 over four quarters signals better demand planning or supply chain compression. A flat or rising DIO often signals demand softness, planning miscalibration, or obsolescence accumulating.
DIO is one of three CCC components: CCC = DSO + DIO - DPO. Each day of DIO reduction shortens the CCC by one day and releases working capital. For a manufacturer with 60 million euros annual revenue and 120 days DIO, reducing DIO to 100 days releases roughly 3.3 million euros in cash (20 days / 365 days x 60 million).
The lever has limits. Cutting DIO too aggressively risks stockouts, lost sales, and rushed expedite fees that erase the working capital gain. The right DIO is the minimum that supports target service levels at acceptable forecast accuracy.
Mistake 1: Optimising DIO at the SKU level only. Total DIO can look healthy while specific high-volume SKUs are chronically out of stock. The metric must be examined by category, channel, and SKU velocity to spot mix-driven distortions.
Mistake 2: Ignoring obsolescence. Inventory that ages past its sellable window stays on the books at cost but is functionally worthless. A clean DIO masks this until the write-down hits. Best-practice teams separate active inventory DIO from total DIO to spot the gap.
Mistake 3: Confusing DIO with inventory turnover. Inventory turnover is the inverse (COGS / Average Inventory, times per year). They convey the same information but the units differ. DIO is more intuitive for working capital discussions; turnover for operational benchmarking.
Mistake 4: Treating DIO as a procurement-only metric. DIO reflects the interaction of demand planning, sales forecasting, supply chain lead times, and manufacturing scheduling. Improving it requires cross-functional alignment, not just procurement targets.
Four levers drive DIO compression:
For finance teams looking to release working capital quickly, DIO reduction typically takes 6 to 12 months to materialise because supply chain changes work through long lead times. The receivables side (DSO) generally responds faster, which is why AI-native AR platforms are often the first lever pulled for working capital improvement.
Days Inventory Outstanding (DIO) is the average number of days a company holds inventory before selling it. It measures how long capital is tied up in inventory and is the inventory component of the Cash Conversion Cycle. The formula is (Average Inventory / Cost of Goods Sold) x Number of Days.
Benchmarks vary widely by industry. SaaS has near-zero DIO. Fast fashion retail runs 30 to 60 days. Standard retail and CPG manufacturing run 60 to 120 days. Industrial manufacturing runs 90 to 180 days. Heavy equipment can be 180 to 365 days. The right DIO is the minimum that supports target service levels without risking stockouts.
DIO and inventory turnover convey the same information but in different units. DIO is days (lower is better, faster turn). Turnover is times per year (higher is better, more turns). Turnover = 365 / DIO. DIO is more intuitive for working capital discussions; turnover for operational benchmarking against industry.
DIO is one of three CCC components alongside DSO (receivables) and DPO (payables). The equation is CCC = DSO + DIO - DPO. Each day of DIO reduction shortens the CCC by one day and releases working capital roughly equal to one day's COGS.
Four levers: demand-driven planning that responds to actual sell-through, lead time reduction with suppliers, SKU rationalisation to cut slow-moving inventory, and vendor-managed inventory programs that shift inventory ownership to suppliers. DIO improvements typically take 6 to 12 months to materialise due to supply chain lead times.
No. Cutting DIO too aggressively risks stockouts, lost sales, and expensive expedite fees that erase the working capital benefit. The right DIO is the minimum that supports target service levels at acceptable forecast accuracy. Going below that breaks the customer experience.
