Inventory Days Calculator
Estimate days inventory outstanding from average inventory and cost of goods sold
Days inventory outstanding
How we calculated it
About the Inventory Days Calculator
Inventory days estimates how many days of cost of goods sold are represented by the average inventory balance. It translates inventory turnover into a time-based measure that is often easier to interpret operationally.
More days can indicate slow-moving stock, but an appropriate level depends on supply lead times, seasonality, service targets and the risk of stockouts.
How to Use the Inventory Days Calculator
- Enter average inventory.
- Enter cost of goods sold for the period.
- Enter the number of days represented by that COGS figure, such as 365 for a full year.
- Calculate inventory days and compare it with prior periods and the operating model.
How the Calculation Works
Inventory days = average inventory ÷ cost of goods sold × days in period.
It is closely related to turnover: when annual turnover is known, approximate inventory days = 365 ÷ inventory turnover.
Worked example
Inventory Days Calculator Worked Example
$150,000 average inventory and $900,000 annual COGS
Inventory days = $150,000÷$900,000×365 ≈ 60.8 days.
Result guide
Understanding Your Inventory Days Calculator Result
About 61 inventory days means the average stock balance represents roughly 61 days of annual COGS at the period’s average rate.
Before you rely on the answer
Assumptions and Limitations
- Average inventory and COGS use the same accounting basis.
- The selected period length matches the COGS period.
- Seasonality and product-level differences may be hidden by the average.
Practical tip
Using This Result in Practice
For seasonal or fast-changing businesses, calculate inventory days by month or product category. One annual average can hide both stockouts and slow-moving excess. A rising inventory-days figure can result from planned stock building ahead of a peak season, not only from weak demand. Compare the trend with sales forecasts and purchase timing before labeling it excess inventory.
Related calculations
Useful Calculations to Continue With
If you want the same relationship expressed as times inventory turns rather than days, use the Inventory Turnover Calculator.
If you want to combine inventory time with receivable and payable timing, use the Cash Conversion Cycle Calculator.
Common questions
Inventory Days Calculator FAQ
What are inventory days?
An estimate of how many days of COGS the average inventory balance represents.
Is lower inventory days always better?
No. Extremely low inventory can create stockouts or production disruptions.
How are inventory days related to turnover?
With annual figures, inventory days are approximately 365 divided by inventory turnover.