Days Inventory Outstanding (DIO): Formula and What It Means
Days inventory outstanding (DIO) measures the average number of days a company holds inventory before selling it. Here is the DIO formula, a worked example, what a good DIO looks like, and how it fits the cash conversion cycle.
Every day a product sits in a warehouse is a day the cash used to make or buy it stays locked up. Days inventory outstanding, or DIO, measures exactly that: the average number of days a company holds inventory before selling it. Alongside days sales outstanding and days payable outstanding, it is one of the three levers that determine how long cash stays tied up in operations.
This guide explains what DIO is, the formula, a worked example, what a good number looks like, and how it fits into the cash conversion cycle.
What is days inventory outstanding?
Days inventory outstanding (DIO), also called days sales of inventory, is the average number of days a company holds its inventory before it is sold. It measures how efficiently a business turns inventory into sales. A lower DIO means inventory moves quickly and cash is not tied up for long; a higher DIO means inventory sits longer, locking up cash and raising the risk of obsolescence.
DIO is a measure of how long your cash is frozen as product on a shelf. Every day of DIO is a day the money you spent on inventory is doing nothing. That is why lean operators obsess over it.
The DIO formula
DIO = (Average Inventory / Cost of Goods Sold) × Number of Days in the Period
For example, with $500,000 in average inventory, $3,650,000 in cost of goods sold for the year, and a 365-day period:
- DIO = ($500,000 / $3,650,000) × 365
- DIO = 0.137 × 365 = 50 days
On average, this company holds inventory for about 50 days before selling it. Cost of goods sold is used (not revenue) because inventory is carried at cost.
What is a good DIO?
There is no universal target, because it depends heavily on industry. A grocery chain or fast-fashion retailer turns inventory in days; heavy machinery or aerospace can hold it for months. A lower DIO is generally better for cash flow, but too low can mean stockouts and lost sales. The most useful comparison is against your own trend over time and your direct industry peers, not an absolute benchmark.
DIO and the cash conversion cycle
DIO is one of the three components of the cash conversion cycle, the number of days it takes to turn money spent on inventory back into cash:
| Metric | What it measures | Effect of a higher value |
|---|---|---|
| DIO (days inventory outstanding) | Time inventory sits before sale | Worse: cash tied up longer |
| DSO (days sales outstanding) | Time to collect from customers | Worse: cash tied up longer |
| DPO (days payable outstanding) | Time to pay suppliers | Better: cash held longer |
The cash conversion cycle is DIO + DSO − DPO. Lowering DIO (selling inventory faster) shortens the cycle and frees up cash, which is why it is a core lever in working capital management.
Why DIO matters
- Cash flow. A lower DIO means less cash frozen in inventory and more available to run the business.
- Efficiency. It shows how well the company matches inventory to actual demand.
- Risk. A rising DIO can signal weakening demand, overstocking, or growing obsolescence risk.
Frequently asked questions
What is days inventory outstanding (DIO)?
DIO is the average number of days a company holds inventory before selling it. It measures how efficiently inventory is converted into sales, a lower DIO means inventory moves quickly and less cash is tied up.
How do you calculate DIO?
DIO = (Average Inventory / Cost of Goods Sold) × Number of Days in the Period. For example, $500,000 in average inventory on $3,650,000 of annual COGS over 365 days gives a DIO of about 50 days.
What is a good DIO?
It depends on the industry, some businesses turn inventory in days, others in months. A lower DIO is generally better for cash flow, but too low risks stockouts. Compare against your own trend and industry peers rather than an absolute benchmark.
How does DIO fit the cash conversion cycle?
DIO is one of three components. The cash conversion cycle is DIO + DSO − DPO. Lowering DIO by selling inventory faster shortens the cycle and frees cash tied up in operations.
The bottom line
Days inventory outstanding measures how long cash stays frozen as inventory before it sells. Calculate it as average inventory divided by cost of goods sold times days in the period, benchmark it against your trend and peers, and lower it to free up cash, without cutting so deep that you risk stockouts. Together with DSO and DPO, it defines the cash conversion cycle.
If you want AI agents tracking the full cash conversion cycle, DIO, DSO, and DPO, continuously from live data, talk to our team.
