Days Inventory Outstanding (DIO) Calculator
Calculate Days Inventory Outstanding to measure how long inventory sits before being sold.
Enter ending inventory, COGS, and period length.
DIO measures how long inventory sits in your warehouse before it is sold. Fewer days means faster turnover and less capital tied up in stock. More days means you are overstocked or demand has slowed — and either way, cash is sitting on a shelf.
The formula:
DIO = (Ending Inventory / Cost of Goods Sold) x Days
A retailer holding $300,000 in inventory against $3,000,000 in annual COGS has a DIO of about 36 days. Inventory turns over roughly every five weeks.
Industry benchmarks vary enormously. Grocery stores target 15-30 days — fresh produce spoils, so fast turnover is survival. Auto dealerships historically run 60-90 days, which is why floor plan financing exists as its own lending category. Aerospace parts manufacturers sometimes hold inventory for years because the alternative is a grounded aircraft.
A sudden DIO spike usually means one of three things: demand fell and purchasing was not cut fast enough; a product line stalled; or inventory is being built strategically ahead of a supply disruption. Each has a different response.
Seasonality distorts DIO significantly. A Christmas ornament manufacturer running DIO in October looks terrible by the formula but is entirely rational. Always compare DIO to the same quarter in the prior year, not just the previous quarter.
One practical issue with the formula: “ending inventory” can be manipulated by timing. Some companies time large purchases to inflate the denominator at quarter-end. Average inventory — (beginning + ending) / 2 — is more accurate for companies with volatile purchasing cycles.
DIO feeds directly into the cash conversion cycle: CCC = DIO + DSO - DPO. Lower DIO shortens the cycle and reduces how much working capital your business needs to stay liquid.