Days Inventory Outstanding (DIO) Calculator

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 instead of in the bank.

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, because fresh produce spoils and fast turnover is survival rather than optimization. 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 land after the cutoff. Average inventory, meaning (beginning + ending) / 2, is more accurate for companies with volatile purchasing cycles, and you can enter that figure in the box instead.

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.

Fill in the two optional boxes with your DSO and DPO and this page will finish the cycle rather than leaving you to do the arithmetic somewhere else.