Inventory turnover shows how often a seller moves through the value of their average stock during a period. It helps reveal whether cash is cycling through products or sitting on shelves.
How to calculate inventory turnover
Inventory turnover = cost of goods sold ÷ average inventory at cost
Average inventory is usually calculated as:
Average inventory = opening inventory + closing inventory ÷ 2
If your annual cost of goods sold is $60,000 and average inventory at cost is $15,000, your inventory turnover is 4. That means the business sold through the equivalent of its average inventory four times during the year.
Use cost, not selling price
Both parts of the formula should use cost values. Comparing sales revenue with stock cost mixes two different bases and can distort the result. Use the amount paid for products or the accounting cost assigned to them.
Also keep the period consistent. Monthly cost of goods sold should be compared with monthly average inventory, while annual figures should use annual data.
Turnover is not the same as units sold
A high-volume low-cost product and a slow premium product can have different economics. Calculate turnover by category and SKU as well as for the whole store. A single blended number can hide stock that has not moved for months.
A reliable SKU structure makes this analysis easier. See How to Create SKU Numbers for Inventory for a practical system that separates variations and multipacks.
Convert turnover into days of inventory
You can translate turnover into an easier planning measure:
Days of inventory = number of days in the period ÷ inventory turnover
Using an annual turnover of 4 gives about 91 days of inventory. This does not mean every product sells in exactly 91 days; it is an average across the stock included in the calculation.
What is a good inventory turnover?
There is no universal target. The right rate depends on product shelf life, supplier lead time, seasonality, minimum order quantities, demand stability and margin.
Very low turnover can mean overbuying, weak demand or obsolete stock. Extremely high turnover can mean efficient stock use, but it can also signal frequent stockouts and lost sales. Compare your current rate with your own earlier periods and with similar product groups.
Find slow-moving stock
Review each SKU using:
- Units sold in the last 30, 60 and 90 days
- Current quantity and inventory value
- Days since the last sale
- Supplier lead time and minimum order
- Gross and contribution margin
- Return, defect and cancellation rates
Prioritise products that tie up a large amount of cash and have little recent demand. Ten slow units of an expensive product may matter more than fifty low-cost items.
Do not solve every problem with a discount
Before discounting, check whether the listing has weak images, missing specifications, poor search terms or a price that ignores marketplace fees. Improve the offer first when the product still has genuine demand.
If a markdown is necessary, use the Discount & Sale Price Calculator and then check the remaining contribution with the Profit Margin Calculator. A faster sale is not helpful if the promotion creates a loss you did not plan for.
Match reorders to demand and lead time
Turnover describes past movement; a reorder point helps decide when to buy again. For each SKU, combine average daily demand, supplier lead time and a safety buffer.
The Inventory Reorder Point Calculator helps estimate the trigger quantity. Review it when demand, lead time or supplier reliability changes.
Ways to improve inventory turnover safely
- Buy smaller quantities more often when supplier terms allow it.
- Stop automatic reorders for declining products.
- Improve product titles, descriptions and images before cutting price.
- Create useful bundles that pair slow stock with genuinely complementary items.
- Return eligible stock to suppliers where agreements permit it.
- Liquidate obsolete inventory with a clear minimum acceptable margin.
- Remove discontinued items from forecasts after remaining stock is sold.
Watch for seasonal distortion
A year-end stock snapshot can mislead a seasonal seller. Use monthly or quarterly averages when inventory changes sharply before holidays or events. Compare the same season year over year where possible.
A simple monthly inventory report
Track these fields for each SKU:
- Opening and closing units
- Opening and closing inventory cost
- Units sold and cost of goods sold
- Turnover and days of inventory
- Stockout days
- Age of the oldest unit
- Next reorder date and quantity
Final takeaway
Inventory turnover is useful because it connects sales activity with cash tied up in stock. Calculate it using cost values, break it down by SKU, and balance faster movement against the risk of stockouts. The goal is not the highest possible turnover; it is enough stock to serve demand without funding shelves that do not move.