Find how many days, on average, inventory sits before it sells — a core efficiency and cash-flow metric for any business that holds stock.
DIO = (average inventory ÷ COGS) × days in period. Lower means inventory sells quickly and less cash is tied up in stock; too low risks stockouts and lost sales. Ideal levels vary hugely by industry (groceries turn fast, jewelry slow). General information only.
Days inventory outstanding measures how many days, on average, products stay in inventory before selling. It's the flip side of inventory turnover: fewer days means faster-moving stock and less cash frozen in the warehouse. But too few days can mean you're running lean enough to risk stockouts.
DIO = (average inventory ÷ COGS) × days in period
DIO translates your stock level into time: on average, how many days does an item sit on the shelf between the day you pay for it and the day it sells? It divides average inventory by the cost of goods sold for the period, then scales to the number of days in that period. The flip side is inventory turnover, how many times a year the whole stock is replaced. Both come from the same two figures, and the calculator shows both.
Average inventory is $60,000 and cost of goods sold for the year is $400,000. $60,000 ÷ $400,000 = 0.15, and 0.15 × 365 = 54.75 days, shown as 54.8 days and rated "Healthy". Turnover is $400,000 ÷ $60,000 ≈ 6.7 turns a year.
What would cutting that to 45 days be worth? At the same sales, 45 days of stock is 45 ÷ 365 × $400,000 ≈ $49,300. That frees about $10,700 of cash that is currently sitting on shelves, with no new sales required. Turning DIO into dollars this way usually makes the case for or against tighter ordering clearer than the day count alone.
Use cost of goods sold, not revenue, because inventory is carried at cost; dividing by revenue understates DIO whenever there is a markup. Use average inventory, ideally the mean of opening and closing balances or of month-end balances, not a single day's count. A year-end count taken after a big clearance sale will make stock look leaner than it was for most of the year.
There is no universal target. Businesses selling perishable or fast-moving goods typically carry only days or weeks of stock; businesses selling slow, high-value items can reasonably hold months. The useful comparison is with your own past periods and with businesses selling similar goods. A rising DIO with flat sales is the warning sign, because it means stock is building faster than it moves. Very low DIO is not automatically good either: running too lean can mean stockouts, rushed reorders and lost sales that never show up in this ratio.
DIO needs a reliable inventory value at several points in time, and that comes from tracking stock as it arrives and sells, not from an annual count. If you hold stock, a simple inventory tracker that records cost per item and quantity on hand, like the ToolWise consignment and inventory trackers, gives you the averages this formula needs. DIO is also one leg of the cash conversion cycle. Pair it with the days sales outstanding calculator to see how long your cash is really tied up, or check the inventory turnover calculator for the same data viewed as turns.
They're two views of the same thing — DIO in days, turnover in times-per-year. DIO ≈ 365 ÷ turns. Use whichever is more intuitive for your team.
Entirely industry-dependent. Compare to your own trend and close competitors, not a universal number. Falling DIO with steady sales is generally a good sign.
Related: inventory turnover calculator · days sales outstanding calculator · cash conversion cycle calculator · all free calculators.
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Last reviewed: September 2026. Free to use, no signup — Days Inventory Outstanding Calculator by ToolWise Digital.
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