Days inventory outstanding: how inventory ties up cash that could pay suppliers
Use days inventory outstanding to estimate how long inventory sits before sale and connect slow stock with purchasing commitments, supplier terms, and cash availability.
Bottom line
A rising DIO is a cash signal, not an automatic order to cut stock. Review slow items, safety stock, seasonal buys, service levels, and open supplier commitments together. The action may be a smaller reorder, a promotion, a supplier-term change, or a deliberate decision to hold critical inventory.
Is it right for you?
- Use average inventory and COGS from the same period
- Compare DIO by category instead of relying only on a company average
- Separate intentional safety stock from obsolete or slow items
- Review open purchase orders and supplier terms before ordering more
Calculate the days on a consistent basis
A common formula is average inventory divided by cost of goods sold, multiplied by the number of days in the period. Average inventory is often the beginning balance plus the ending balance, divided by two.
Use the same scope for inventory and COGS. Mixing one location's inventory with companywide COGS creates a precise-looking number that cannot guide a purchase decision.
Read the trend with stock availability
| DIO movement | Possible cause | Next check |
|---|---|---|
| Rising with stable sales | Overbuying or slow items | SKU aging and open POs |
| Falling with stockouts | Inventory cut too far | Lost sales and expedite costs |
| Rising before peak season | Planned build | Forecast, sell-through date, and cash plan |
| Sudden jump at close | Count, cutoff, or cost issue | Inventory reconciliation and late invoices |
Connect the ratio to AP decisions
Inventory consumes cash before customers pay for the finished sale. Compare DIO with supplier due dates, open purchase orders, available cash, and the AR collection forecast; the supplier side of that comparison is what days payable outstanding measures directly.
A volume discount is not a saving if the extra units sit unsold, expire, or force expensive financing. Ask purchasing to show the cash date as well as the unit-price reduction.
Frequently asked questions
Is lower DIO always better? No. Too little inventory can cause stockouts, missed sales, and expensive emergency orders.
What period should be used? Use a period that matches the business cycle and apply it consistently; seasonal businesses should compare similar periods.
Why review by category? Fast-moving products can hide obsolete or slow stock elsewhere.
What should a rising DIO trigger? Look at aged stock, forecasts, open POs, what is already promised to suppliers, and the cash forecast before approving more purchases.
What's the best way to bring DIO down? Start with SKU-level aging data instead of a blanket order cut. Clear or discount genuinely obsolete stock, tighten reorder points on slow movers while protecting safety stock on anything with a real service requirement, negotiate smaller and more frequent supplier batches instead of large infrequent ones, and time promotions to move stock before it ages rather than after. The section above on tying DIO to AP timing covers why cutting inventory blindly can cost more in stockouts than it saves.
What is DSO, DOH, and DPO? Three related cash-cycle metrics, not interchangeable names for the same thing. DSO (days sales outstanding) tracks how long customers take to pay after a sale. DOH (days on hand) is another name for DIO: the length of time stock waits in the warehouse before a sale happens, which is what this page covers. DPO, the payables-side counterpart already linked above, tracks how long the business itself takes to settle supplier bills. All three combine into the cash conversion cycle.
We wrote a dedicated breakdown of this in Fiscal year, worth a look if it applies to your setup.
That situation deserved its own writeup: General ledger.