Days Inventory Outstanding (DIO) measures the average number of days a company holds inventory before selling it. It is the third leg of the cash conversion cycle, alongside Days Sales Outstanding (DSO) and Days Payable Outstanding (DPO), and it specifically captures how efficiently a business turns its inventory investment into sales.
FORMULA
Days Inventory Outstanding = (Average Inventory ÷ Cost of Goods Sold) × Number of Days in Period
EXAMPLE
A distributor carries $420,000 in average inventory against $2,520,000 in annual cost of goods sold.
DIO = ($420,000 ÷ $2,520,000) × 365 = 61 days.
On average, inventory sits for about two months before it sells.
Average inventory is typically (beginning inventory + ending inventory) ÷ 2 for the period measured, which smooths out timing spikes from a single snapshot.
A lower DIO generally means inventory is moving faster, which frees up cash and reduces the risk of holding obsolete or excess stock. A higher DIO means cash is tied up longer in goods sitting on shelves, which is not automatically bad, some businesses deliberately hold more inventory to avoid stockouts, but it does represent a real cost.
DIO varies enormously by industry and should be benchmarked against a company's own trend and its direct peers rather than any universal target. A grocery distributor and a heavy equipment dealer have entirely different natural inventory cycles, and comparing one against the other tells you nothing useful.
FORMULA
Cash Conversion Cycle = DIO + DSO − DPO
DIO is the first of the three inputs, representing how long cash is tied up before inventory even converts to a sale. It combines with DSO, how long customers take to pay after that sale, and DPO, how long the business takes to pay its own suppliers, to give the full picture of how long cash is locked in operations.
EXAMPLE
A distributor with 61 days DIO, 40 days DSO, and 30 days DPO has a cash conversion cycle of 61 + 40 − 30 = 71 days. Reducing DIO by 10 days, through tighter purchasing or faster turnover, shortens the cycle by the same 10 days without touching collections or payment terms at all.
DIO is a purchasing and demand-planning metric more than an accounts payable one, but it belongs in the same conversation as DPO and DSO because all three compete for the same finite amount of working capital.
