What is Days Inventory Outstanding (DIO)?
Days Inventory Outstanding (DIO) shows the average number of days inventory stays on the balance sheet before flowing through cost of goods sold.
It links inventory management to the cash conversion cycle by translating inventory turnover into time, making it clear how long cash is locked up in stock instead of funding growth, debt reduction, or dividends.
A lower DIO generally signals:
- Faster inventory turnover
- Leaner working capital and higher free cash flow
- Less risk of obsolescence, discounting, or write-downs
A higher DIO usually points to:
- Slow-moving or obsolete items
- Over-ordering relative to demand
- Capital tied up in stock instead of in higher-return uses
Formula
Standard, COGS-based definition (most common in corporate finance):
Where:
- Average Inventory = (Beginning Inventory + Ending Inventory) / 2
- COGS = Cost of Goods Sold over the period (at cost, not selling price)
- Period Days = Number of days in the period (often 365, 360, 90, or 30)
Equivalent form using the inventory turnover ratio:
If only Net Sales is available and COGS is missing, some practitioners approximate DIO by using sales instead of COGS:
This Net Sales version gives an approximate “days of inventory” and should be interpreted with caution, since it mixes cost-based inventory with revenue.
Example
A company wants to understand how efficiently it is managing stock over a full year (365 days):
- Beginning inventory: $50,000
- Ending inventory: $55,000
- COGS for the year: $500,000
- Compute average inventory:
- Compute inventory turnover:
- Compute DIO (days inventory outstanding):
Interpretation: the business holds, on average, about 38 days of inventory before it is consumed as COGS. Compared with peers or internal targets, management can decide whether to reduce safety stock, shorten reorder cycles, or improve demand planning to free up working capital and strengthen the overall cash conversion cycle.