Safety Stock & Stockout Probability Calculator
Calculate safety stock and stockout probability for your inventory instantly. Free, accurate tool for supply chain and procurement professionals.
Safety stock calculator
Stockout probability
How to calculate safety stock
Safety stock is the extra inventory kept to protect against uncertainty in demand and lead time. It helps prevent stockouts and lost sales. The standard formula is:
Safety Stock = Z × σdemand × √LeadTime
Where Z is the standard normal value for your target service level (e.g., 1.65 for 95%), σdemand is the demand standard deviation, and LeadTime is the replenishment period. This calculator uses textbook formulas to help you set the right safety stock for your business or class project.
Example: If your average demand is 100 units/week, lead time is 10 weeks, demand standard deviation is 20, and you want a 95% service level, your safety stock is about 104 units.
Frequently Asked Questions
Use the formula: Safety Stock = Z × σdemand × √LeadTime. Enter your demand standard deviation, lead time, and target service level to get the Z value. This tool does it for you instantly.
The right service level depends on your business goals and risk tolerance. Common values are 90%, 95%, or 99%. Higher service levels mean more safety stock and lower risk of stockouts, but higher inventory costs.
Higher demand variability (standard deviation) increases safety stock. If your demand is stable, you need less safety stock. Use the slider to see how changes in variability impact your results.
Stockout probability is the chance you will run out of stock during lead time. It is the inverse of your service level. This tool estimates your risk based on your safety stock and demand variability.
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