What is days inventory outstanding?
DIO tells you the average number of days inventory sits before it sells, and a lower number means your stock is moving faster. It answers a simple operational question: how long does product wait on the shelf before it becomes revenue?
Inventory ties up working capital, so DIO shows how much cash is stuck on your shelves and how that affects cash flow. Money sitting in unsold stock is money you can’t spend on payroll, materials, or growth.
The scale of that trapped cash is easy to underestimate. As of July 2026, U.S. businesses held $1.30 in inventory for every $1 of monthly sales, according to the U.S. Census Bureau, which shows just how much capital inventory can represent.
You may also see this ratio called days sales in inventory (DSI) or days in inventory. They all describe the same measurement.
Key characteristics
- The formula: DIO = (Average inventory / cost of goods sold (COGS)) x 365 days.
- Lower is usually better: faster turnover means less capital tied up, plus lower carrying and obsolescence costs.
- Higher can signal trouble or be strategic: a high number often points to overstocking or slow sales, though sometimes it’s intentional for goods with a long shelf life or an expected demand spike.
- Compare only within an industry: food companies average around 6 days while steel averages around 50, so measuring across industries will mislead you.
- DIO is the inverse of the inventory turnover ratio: same idea, expressed in different units.
- Both extremes cost money: overstocks and stockouts together, which IHL Group calls inventory distortion, reached $1.7 trillion globally in 2026, equal to 6.2% of global retail sales.
Example
Picture a company with average inventory of $500,000 and COGS of $2,000,000. Running the numbers gives you ($500,000 / $2,000,000) x 365, which works out to about 91 days.
At 91 days, that stock sits on the higher side for many sectors, which suggests cash is idling longer than it needs to. Teams can pull that number down with inventory optimization techniques such as just-in-time ordering, demand forecasting, and reorder points.
Seeing your stock levels as they change also helps. Real-time inventory control gives you the visibility to catch slow movers early and keep DIO in a healthy range.
Related terms
FAQ
What does DIO stand for?
DIO stands for days inventory outstanding, the average number of days a company holds inventory before selling it.
What does a high days inventory outstanding mean?
A high DIO means inventory sits longer before selling, often signaling overstocking, slow sales, or cash tied up in stock, though some industries run high DIO by design.
How is DIO different from inventory turnover?
They measure the same efficiency in different units: turnover counts how many times you sell through inventory in a period, while DIO expresses it as a number of days.