Stockout Cost Calculator
Estimate the true cost of running out of stock — lost margin, expedite costs, and the longer-term customer loss that most calculations omit.
🚫 Inventory📐 Stockout cost = lost margin + expedite costs + customer lifetime value lost💼 Business
Units of demand unmet
Contribution margin per unit
Share of customers who buy later (%)
Share who switch permanently (%)
Customer lifetime value
Expedite / emergency restock cost
Please enter valid values.
Formula & Reference
| Variable | Symbol | Formula | Units |
|---|---|---|---|
| Stockout Cost Calculator | — | Stockout cost = lost margin + expedite costs + customer lifetime value lost | currency |
Step-by-Step Examples
Example 1
Typical Retail Stockout
250 units unmet, 18 margin, 40% backorder, 15% lost permanently, CLV 340, expedite 1,200.
- Recovered = 250 × 40% = 100 units
- Immediate lost margin = 150 × 18 = 2,700
- Customers lost = 250 × 15% = 37.5, × 340 = 12,750
- Total = 2,700 + 12,750 + 1,200 = 16,650
✓ 16,650 — 66.60 per unit of stockout
Example 2
Margin-Only View
Same stockout counting only lost margin.
- Lost margin alone = 2,700
- This is what most stockout calculations report
- It understates the true cost by more than six times
✓ 2,700 — the number that misleads
Example 3
Loyal Customer Base
250 units unmet, 18 margin, 85% backorder, 2% lost, CLV 340, no expedite.
- Recovered = 212.5 units
- Immediate lost margin = 37.5 × 18 = 675
- Customers lost = 5, × 340 = 1,700
- Total = 2,375
✓ 2,375 — loyalty limits the damage
Real-World Applications
Safety Stock Justification
Quantifying stockout cost is what justifies carrying safety stock, which otherwise looks like pure expense.
Service Level Setting
Comparing stockout cost against holding cost determines the economically optimal service level.
Hidden Customer Loss
The permanent customer loss component typically dwarfs immediate lost margin, yet is routinely omitted.
Prioritisation
Stockout cost per unit varies by product, showing which items warrant the tightest availability.
Common Mistakes to Avoid
⚠️
Counting only the lost sale
As the examples show, immediate lost margin can be a small fraction of true cost once permanent customer loss is included.
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Assuming all demand is backordered
In competitive categories with easy substitution, a large share of customers simply buy elsewhere and may not return.
⚠️
Ignoring reputational and search effects
In ecommerce, out-of-stock listings can lose search placement and reviews, with effects that persist beyond the stockout itself.
Frequently Asked Questions
What does a stockout actually cost? ▾
Lost contribution margin on unrecovered sales, expedite costs to restock, and the lifetime value of customers who switch permanently.
How do I estimate the permanent loss rate? ▾
Post-stockout cohort analysis is best. Absent that, category substitutability is the main guide — commoditised products lose more customers.
Why does stockout cost matter for inventory decisions? ▾
Because safety stock only looks expensive until compared against stockout cost. The comparison determines the economically right service level.
Do stockouts affect ecommerce differently? ▾
Often more severely, since substitution is a click away and out-of-stock listings can lose marketplace search ranking that takes time to recover.
Should stockout cost vary by product? ▾
Yes. High-margin, high-CLV, and easily substituted products all carry higher stockout costs and justify higher service levels.