Hong Life CalculatorsUnderstanding the inventory shrinkage unit cost calculator — concept and principle
Inventory shrinkage is stock you paid for but cannot sell because it was damaged, spoiled, stolen, miscounted or lost. This calculator shows the true cost of each unit you actually sell once those losses are spread over the remaining stock. Retailers, food businesses and online sellers use it to set prices that still protect their margin. It works with any currency.
How it is calculated
- True cost per sellable unit = unit cost ÷ (1 − loss rate ÷ 100)
- Extra cost per unit = true cost − unit cost
Unit cost is what you pay per unit bought. Loss rate is the percentage of units bought that never get sold.
The principle
If you buy 100 units and 3 are lost, you paid for 100 but can sell only 97. The total cost is still 100 × unit cost, so each sellable unit must carry 100 ÷ 97 of the original cost, which is unit cost ÷ (1 − 0.03). This is why the calculator divides rather than simply adding 3%: multiplying by 1.03 underestimates the effect, and the gap widens as the loss rate grows. At a 50% loss rate, for example, each sold unit costs double, not 1.5 times.
Worked example
- Unit cost = 12 USD, loss rate = 3%.
- True cost = 12 ÷ (1 − 0.03) = 12 ÷ 0.97 = 12.371 → 12.37 USD.
- Extra cost = 12.371 − 12 = 0.371 → 0.37 USD per unit.
- Check: 100 units cost 1,200 USD; 97 sellable units × 12.371 ≈ 1,200 USD.
How to read the result
The extra cost is how much each sale must recover just to cover losses. Use the true cost, not the purchase price, when you calculate markup, gross margin and break-even prices. Shrinkage is typically a small percentage of sales in general retail, but it can be far higher for fresh food, fragile goods or high-theft items, so measure your own rate by category from stock counts.
Common mistakes
- Adding the loss percentage to cost instead of dividing by (1 − loss rate).
- Using shrinkage as a share of sales value when the formula needs a share of units bought.
- Applying one store-wide rate to categories with very different losses.
Frequently asked questions
How do I measure my shrinkage rate?
Compare the stock you should have (opening stock + purchases − recorded sales) with a physical count. The missing share is your shrinkage.
Does shrinkage include items sold at a discount?
Usually not. Markdowns reduce revenue rather than units; this calculator covers units that are not sold at all.
Can I use this for manufacturing scrap?
Yes. The same logic applies to yield loss: input cost ÷ (1 − scrap rate) gives the cost per good unit.
Sources: National Retail Federation, National Retail Security Survey