Inventory Turnover
Inventory turnover measures how many times the average inventory investment is sold through during a defined period, using cost-based values.
What is Inventory Turnover?
The ratio compares the cost of goods sold with the average stock held at cost. It describes the pace at which inventory supports sales, rather than the percentage of a specific delivery that sold. That latter question belongs to sell-through.
Turnover is reported as a multiple, such as 4× per year. The period is part of the meaning: 4× annually and 4× quarterly are very different stock cycles. Always label the interval.
Inventory turnover = Period COGS ÷ Average inventory at cost
A basic average is (opening inventory + closing inventory) ÷ 2. More frequent stock observations give a better average when balances are seasonal or volatile.
Four turns across a year
A store records $240,000 of annual COGS and holds an average of $60,000 in inventory at cost. Turnover is 4× per year. Using a 365-day convention, average inventory days are approximately 365 ÷ 4 = 91.25 days. This is an aggregate estimate, not the age of every unit.
How to interpret it
A higher ratio can mean less average stock is supporting the same sales cost. It can also reflect inventory being too lean, with stockouts restricting availability. Turnover should therefore be interpreted with service levels, lead times and lost-sales evidence.
A low ratio can indicate slow demand, overbuying or obsolete goods. It can also occur when a seasonal business builds inventory ahead of its selling period. Comparing the same seasonal stage is more informative than comparing an arbitrary month with a peak month.
The aggregate can hide uneven performance. Fast-selling products may compensate for inactive stock in the overall ratio. A healthy store-level number does not establish that every SKU is using inventory capital well.
Keep the valuation basis stable. COGS and average inventory both use cost; dividing retail sales by inventory at cost creates a different ratio influenced by markup. Large write-downs or stock adjustments can also change the metric independently of ordinary selling speed.
Common mistakes
Using only closing stock in a seasonal business
A low balance on the final day may be unrepresentative of the stock held throughout the period. Use an average that reflects the actual trading cycle.
Assuming faster is always better
Very high turnover can coexist with insufficient availability. The metric describes movement relative to investment, not an instruction to eliminate stock buffers.