Irish Calculators
Business

Inventory Turnover and Inventory Days Calculator

Measure how often inventory cost turns over and its equivalent holding days. Use matching cost bases and reporting periods; zero cost of goods sold has no finite inventory-days result.

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Your numbers

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How the calculation works

Measure how often average inventory is consumed through cost of goods sold during a reporting period. The tool also expresses that relationship as inventory days using the period length you supply.

Inventory turnover = period cost of goods sold / average inventory. Inventory days = period length in days / inventory turnover.

  1. Establish average inventory

    Endpoint mode adds opening and closing inventory and divides by two. Known-average mode uses your supplied average, which may better represent seasonal or uneven holdings.

  2. Calculate turnover

    Divide period COGS by positive average inventory. The result is the number of inventory turns associated with that reporting period, not automatically an annualised measure.

  3. Translate turnover into days

    Divide reporting-period days by turnover. With zero COGS, turnover is zero and no finite inventory-days result exists; zero days would misstate the position.

Worked example: Annual turnover

Sample inputs demonstrate the method. They are not a forecast or product offer.

Opening inventory of €20,000 and closing inventory of €28,000 average €24,000. COGS of €120,000 gives five turns. With a 365-day reporting period, the example inventory-days measure is 365 divided by five, or 73 days.

Cost of goods sold for the period
120000
Inventory average input
Opening and closing inventory
Opening inventory
20000
Closing inventory
28000
Days in the reporting period
365

Expected result

Inventory turnover
5
Inventory days
73
Worked example: Quarterly turnover

Sample inputs demonstrate the method. They are not a forecast or product offer.

Cost of goods sold for the period
60000
Inventory average input
Known average inventory
Average inventory
15000
Days in the reporting period
90

Expected result

Inventory turnover
4
Inventory days
22.5

Understanding your result

Inventory days is a ratio-based measure of stock relative to consumption at cost. It does not track the actual age of each item or guarantee that every item will sell within that interval.

A higher turnover can reflect efficient stock use or constrained availability. Consider stockouts, product mix and seasonality before interpreting a change as unequivocally better performance.

Questions you might have

Can I use sales instead of cost of goods sold?

That would compare selling-price revenue with cost-valued inventory and produce a different ratio. Use COGS for this cost-based turnover measure.

Choosing the right inputs

Cost of goods sold for the period
Use cost of goods sold for the selected period, not sales revenue. Inventory and COGS need the same valuation basis and business scope.
Inventory average input
Use opening and closing balances for a simple two-point average, or enter a separately established average when stock fluctuates substantially within the period.
Days in the reporting period
Enter the actual reporting-period length used for these figures. A quarterly COGS total should not silently be combined with a full year's day count.

Common mistakes to avoid

  • Do not divide selling-price revenue by inventory carried at cost and label it this cost-based turnover measure.
  • Do not rely on a two-date average when those dates systematically omit the year's peak stock holdings.

Assumptions to check

  • Use amounts in one currency and one reporting period. Results are labelled EUR; the arithmetic also works for another consistent currency.
  • Inventory and cost of goods sold must share a cost basis and reporting scope. Zero COGS produces zero turnover and no finite inventory-days measure.

Sources and method

Read our calculation and testing approach.