Safety Stock Calculator With Service Level
Enter your average demand, how much it varies, your average lead time and how much that varies, then pick a service level. You get the safety stock and the reorder point that cover the risk.
Results
- Safety stock (units)
- 73
- Reorder point (units)
- 273
- Expected demand during lead time
- 200
- Z-score used
- 1.64
Frequently asked questions
What is the safety stock formula?
When both demand and lead time vary, safety stock is the z-score times the square root of (lead time times demand variance plus average demand squared times lead-time variance).
What z-score goes with each service level?
A 90% service level uses a z-score of 1.28, 95% uses 1.64, 98% uses 2.05 and 99% uses 2.33. A higher service level needs more safety stock.
What is the difference between safety stock and reorder point?
Safety stock is the buffer for surprises. The reorder point is the expected demand during lead time plus that buffer, and it tells you when to place the order.
How do I find my demand standard deviation?
Take your daily unit sales for the last 30 to 90 days and compute their standard deviation in a spreadsheet using the STDEV function.
Related tools
Sources and assumptions
Demand and lead time are independent and roughly normally distributed.
Estimates for planning, not financial advice. Check current rates with your provider.