Key Takeaway: Safety stock is the buffer between normal operations and the day a supplier is late or demand spikes unexpectedly. Too little, and you stock out. Too much, and you're just holding dead capital.
What's on This Page
The Formula
Worked Example
Maximum daily sales: 12 units. Maximum lead time: 14 days. Average daily sales: 8 units. Average lead time: 10 days.
Why Both Numbers Matter
This formula buffers against two different risks at once: demand spiking above average, and your supplier taking longer than usual. Using only average figures ignores the fact that "average" delay and "average" demand rarely both happen on your worst day. Occasionally both do, and that's exactly when you'd stock out without this buffer.
Tuning Safety Stock Over Time
- Higher for SKUs with unreliable or long-lead-time suppliers
- Higher for your highest-revenue (A-tier) SKUs, where a stockout costs the most
- Lower for slow-moving, low-value SKUs where the cost of a stockout is minor
This number feeds directly into your reorder point calculation.
For further reading, see the Association for Supply Chain Management (ASCM).
Checklist
- Identify maximum daily sales for the SKU over a recent period
- Identify maximum realistic supplier lead time
- Identify average daily sales and average lead time
- Apply the safety stock formula using both maximum and average figures
- Adjust the buffer higher for A-tier or unreliable-supplier SKUs
- Feed the result into the SKU's reorder point calculation
Common Mistakes
FAQ
Does every SKU need the same amount of safety stock?
No. A-tier, high-value SKUs and those with unreliable suppliers generally deserve more buffer than slow-moving, low-value ones.
What happens if safety stock is set too low?
The business becomes vulnerable to stockouts whenever demand spikes or a supplier is late, even briefly.
What happens if it's set too high?
Excess capital gets tied up in stock that mostly just sits as insurance, adding carrying cost without proportional benefit.
How does safety stock relate to the reorder point?
Safety stock is one input into the reorder point formula. It's the buffer added on top of expected demand during lead time.
Calculate This For Your Business
Related Guides in the Inventory Academy
- Reorder Point Guide. where this safety stock number gets used
- ABC Inventory Analysis. deciding which SKUs deserve a bigger buffer
- Why Inventory Mistakes Destroy Small Businesses. another guide in the Inventory Academy