Inventory ties up cash before it becomes a completed sale. Too much stock can increase storage, expiry and obsolescence risk, while too little may create stockouts and lost orders. Turnover helps compare the pace of inventory movement, but it must use consistent units, periods and valuation. A high figure is not automatically good if it reflects frequent shortages, and a low figure can be normal for seasonal or specialised products.
Formula and definitions
Formula: Inventory turnover = cost of goods sold ÷ average inventory; days inventory ≈ days in period ÷ turnover
Use average inventory
The opening and closing balances can differ substantially around a seasonal peak or bulk purchase. A simple average of opening and closing inventory may be adequate for a stable business, but monthly or weekly averages give a better view when stock swings sharply. Use the same accounting valuation and currency across the period. If inventory is written down, transferred or counted with a different method, document the change before comparing turnover with an earlier period.
Keep the numerator and denominator aligned
Turnover usually uses cost of goods sold divided by average inventory at cost, not sales revenue divided by inventory at retail price. Revenue includes the markup, so using it can inflate the result and make comparisons unreliable. Match the cost period with the inventory valuation and explain any exclusions, such as work in progress or consigned stock. A consistent formula matters more than the number of decimal places.
Interpret turnover with service levels
Faster turnover can release cash and reduce carrying costs, but a very high figure may indicate that replenishment is too slow or safety stock is inadequate. A low figure can signal overbuying, slow demand or a long replenishment cycle, but it can also be appropriate for expensive spare parts. Check stockouts, fulfilment delays, discounts, spoilage and purchase lead times beside the turnover metric.
Use days inventory to plan replenishment
Days inventory provides an approximate translation of turnover into time. It is not an expiry guarantee or a precise date until every item sells; products move at different rates. Segment inventory by product family and use demand forecasts plus lead-time variability. Avoid using one warehouse-wide average to set reorder points for both a fast-selling basic item and a seasonal specialist product.
Worked example
A shop records $240,000 of cost of goods sold over a 360-day internal reporting period. Average inventory at cost is $40,000. Turnover is 6 times per period and days inventory is about 360 ÷ 6 = 60 days. If stockouts also rise, simply pushing turnover higher could make service worse; review lead times and item-level demand before cutting average inventory further.
| Item | Calculation or value | Meaning |
|---|---|---|
| Cost of goods sold | $240,000 | Matching period |
| Average inventory at cost | $40,000 | Opening/closing average |
| Turnover | 6 times | COGS ÷ average inventory |
| Days inventory | 60 days | 360 ÷ turnover |
Common mistakes
Do not use retail sales in the numerator against inventory valued at cost. Do not compare a 360-day turnover figure with a 365-day figure without noting the convention. Avoid treating the entire inventory pool as homogeneous when demand, margin and replenishment time vary widely.
Next steps
Calculate turnover from consistent financial records, then segment it by product and compare with stockouts, spoilage and supplier lead times. Use the trend to ask better questions about ordering and working capital rather than enforcing a universal target across different categories.
Frequently asked questions
Is higher turnover always better?
No. It may reduce holding cost but also indicate insufficient stock or missed sales.
Why use average inventory?
It reduces the distortion from a single end-of-period stock balance, especially after a bulk purchase or seasonal build.
Related tools and guides: Business break-even guide · Cash-flow forecast · Calculate turnover