Safety Stock
Extra inventory kept as a buffer against unexpected demand spikes or supply disruptions.
1 min readLast updated Apr 2026
Quick Reference
CategoryFulfillment & Operations
Related Terms2
Extra inventory kept as a buffer against unexpected demand spikes or supply disruptions.
Why It Matters
Safety stock prevents stockouts when demand exceeds forecasts or supply chain hiccups occur. The cost of carrying extra inventory is almost always less than the cost of lost sales, disappointed customers, and damaged ad campaign ROAS when products go out of stock.
Practical Example
Scenario
A supplements brand calculates safety stock for their bestselling product.
Calculation
Average daily sales: 50 units. Standard deviation: 15 units. Desired service level: 95% (z=1.65). Lead time: 14 days. Safety stock = 1.65 × 15 × √14 = 93 unitsResult
Keeping 93 extra units means 95% probability of not stocking out during any lead time period—costing $1,400 in carrying cost but preventing $12,000+ in lost sales per occurrence.
Pro Tips
- 1Calculate safety stock per SKU—bestsellers need more, slow movers less
- 2Increase safety stock during high-variability periods (holidays, promos)
- 3Factor in supplier reliability—unreliable suppliers need higher buffers
- 4Review safety stock quarterly as demand patterns change
Common Mistakes to Avoid
Using the same safety stock formula for all products (one size doesn't fit all)
Not increasing buffer before major campaigns or seasonal peaks
Carrying safety stock on dead inventory (wasted capital)