Inventory turnover and inventory days calculator
Measure stock efficiency and days held.
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How it works
Measure how quickly inventory moved during a defined historical period. Turnover compares the cost of stock sold with average stock held at cost; inventory days expresses the same relationship using the actual period length. Xero’s inventory guidance uses COGS divided by average inventory, while its Analytics calculations scale inventory days to the number of days in the reporting period.
A few things to know
A historical average that does not forecast demand or model SKU-level stockouts, lead times, safety stock, seasonal purchases, write-downs, or changing costs. Opening/closing inventory averages can hide large movements within the period. Keep COGS and inventory on a consistent cost basis and currency. Average inventory must be positive; zero COGS produces zero turns and no finite inventory-days estimate. Display rounding does not change calculations.
Results use your inputs. Keep all money amounts in the same currency.
When to use this tool
Inventory turnover and inventory days describe the relationship between stock held and stock sold during the same reporting period. Use this calculator to translate your cost-of-goods-sold report and average inventory balance into a period turnover ratio and a days measure. It is particularly useful when comparing quarters of different lengths or checking whether stock investment is growing faster than sales activity.
- Review a product category before committing cash to another supplier order.
- Compare a 90-day quarter with another period while keeping cost valuation and period length consistent.
- Prepare an inventory review that explains both stock turns and the amount of time represented by average stock.
How to use inventory turnover and inventory days calculator
Choose the reporting window
Enter the actual number of days in the period and pull COGS for precisely those dates. For example, use 90 days for a 90-day quarter rather than leaving the calculation on a 365-day basis.
Enter stock at its cost value
Use average inventory held during that window. A simple starting estimate is opening inventory plus closing inventory, divided by two. If stock levels changed sharply, an average of more frequent balances is usually more representative.
Read both measures together
Calculate period turns and inventory days, then download the CSV for your purchasing review. Investigate changes by SKU or category before deciding that a higher turnover is necessarily better.
Six turns in a 90-day quarter
Inputs
Period COGS: 300,000. Average inventory at cost: 50,000. Period length: 90 days.
Result
Inventory turnover is 6× for the quarter. Inventory days are 15. Average daily COGS is 3,333.33.
What it means
Average stock held represents about 15 days of the quarter’s COGS rate. The 6× result belongs to the entered quarter; it is not six annual turns or a promise that every individual item sells in 15 days.
Common mistakes to avoid
Mixing sales prices and stock costs
Sales revenue includes markup while inventory is normally carried at cost. Using sales revenue in place of COGS changes the ratio and makes comparisons misleading.
Using one stock snapshot as the average
A closing balance immediately after a delivery can overstate normal stock held. A balance taken just before restocking can understate it. Review more frequent balances when purchasing is uneven.
Treating days as a reorder rule
This aggregate historical measure does not include supplier lead times, safety stock or SKU demand. A low overall days result can coexist with slow stock and shortages in different products.
Frequently asked questions
Definitions, edge cases, and practical next steps for this tool. Search all tool FAQs ↗
How is inventory turnover calculated?
Divide COGS for the measured period by average inventory at cost for that same period. With 300,000 of COGS and 50,000 of average stock, turnover is 6. Keep the cost basis and dates aligned so that the numerator and denominator describe the same operation.
What is the difference between turnover and inventory days?
Turnover expresses the relationship as the number of stock turns during the period. Inventory days expresses it as period days divided by turnover. In the example, 90 ÷ 6 gives 15 days. They are two views of the same inputs rather than independent performance scores.
Should I always use 365 days?
Use 365 only when your COGS covers a 365-day reporting period. For a month, quarter or leap-year window, enter the actual day count. A 90-day COGS figure combined with 365 days would overstate this calculation’s inventory-days result by using mismatched time periods.
Can I use opening and closing inventory to find the average?
Yes: add the opening and closing cost balances and divide by two as a simple approximation. If you begin with 40,000 and end with 60,000, enter 50,000. For irregular deliveries or a seasonal peak, consider averaging daily or monthly balances instead of relying on two endpoints.
What happens if no stock was sold?
With positive average inventory and zero COGS, turnover is zero. There is no finite days estimate because average daily COGS is zero. The tool reports that directly. Do not replace zero with a small invented sales amount simply to obtain a finite result.
Why must average inventory be greater than zero?
Turnover divides by average inventory, so a zero balance makes that ratio undefined. If COGS is positive while your reported average inventory is zero, check rounding, drop-shipping activity and the balance definition. This calculator is designed for inventory you actually hold at a measurable cost value.
Is a higher inventory turnover always better?
Judge it alongside availability, margin, supplier timing and customer service. Selling quickly can release working capital, but insufficient stock can also create missed orders. Compare the same category over time and investigate availability problems before reducing inventory solely to improve the ratio.
What should I do after the calculation?
Separate the total into useful categories or SKUs, compare matched periods and inspect obsolete stock and upcoming replenishment dates. Pair this ratio with landed cost to understand cash tied up in inventory. The CSV preserves the assumptions so the next review uses a comparable basis.
Explore the topic in the blog
Sources and method
Use the references below to check definitions and platform guidance. The model’s scope and limits are explained above. Read our editorial standards.