Inventory Days Calculator (DIO)
Calculate Inventory Days step by step: average inventory ÷ cost of goods sold × days in period.
In short
Formula: Days inventory outstanding = average inventory ÷ cost of goods sold × days in period.
What this calculator does
Calculate Inventory Days step by step: average inventory ÷ cost of goods sold × days in period. Worked example, questions and limitations included.
Use it to turn Currency (symbol only, never converted), Average inventory value, Cost of goods sold for the period, Days in the period into a checked result you can compare, copy, or rerun with different assumptions.
The page shows the formula, a numeric worked example, and the assumptions that affect this inventory calculation.
Inputs and what they mean
- Currency (symbol only, never converted)
- — choice value.
- Average inventory value
- — number value.
- Cost of goods sold for the period
- — number value.
- Days in the period
- — number value.
How to use it
- Enter each value in the unit shown next to the box (use the unit converter first if your numbers are in other units).
- Check the breakdown to see every intermediate step.
- Read the limitations before relying on the result.
Formula
Standard working-capital ratio (OpenStax Principles of Accounting).
Enter the period length yourself (365, 360 or the days in the month) — no convention is assumed.
Equivalent to days in period ÷ inventory turnover.
Days inventory outstanding = average inventory ÷ cost of goods sold × days in period.
Inputs used: Currency (symbol only, never converted), Average inventory value, Cost of goods sold for the period, Days in the period.
Worked example
Annual DIO
- 100,000 ÷ 600,000 = 0.1667.
- × 365 = 60.83 days.
Reading the result
The headline figure is the main answer. Any breakdown underneath shows the parts that make it up, so you can check the working and see what changes when you adjust an input.
Limitations and assumptions
- Backward-looking.
- Average inventory hides peaks.
- Value-based, not unit-based.
- Results are planning estimates built only from the figures you enter. No prices, rates, demand patterns or service levels are built in, and the results are not supplier quotes or carrier rates.
- The result depends on the values you enter for this inventory days calculator (dio); it does not supply missing rates, rules, prices, dates, or assumptions for you.
Common questions
Is lower always better?
Lower ties up less cash, but too low risks stock-outs. Check the formula, example, and limitations on this page before using the result for a real inventory decision.
365 or 360 days?
Use whatever your organisation reports with; just be consistent. Check the formula, example, and limitations on this page before using the result for a real inventory decision.
Is this the same as stock coverage?
No. DIO looks back at average cost; stock coverage looks forward at current stock versus expected demand.
How do I use the Inventory Days Calculator (DIO)?
Enter the required values for Currency (symbol only, never converted), Average inventory value, Cost of goods sold for the period, Days in the period. The calculator applies the formula on this page and shows the main result with any supporting breakdown so you can check the arithmetic.
What formula does the Inventory Days Calculator (DIO) use?
Days inventory outstanding = average inventory ÷ cost of goods sold × days in period. The visible formula section above lists the calculation path and the edge cases the page handles, so the result can be checked without relying on the form alone.
Can the Inventory Days Calculator (DIO) be used for exact decisions?
Use it as a calculation aid, not as a substitute for checking the underlying rule, contract, policy, or professional advice that applies to your situation. When a result depends on local rules, personal details, prices, or dates, enter those values yourself and confirm them before acting.
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