Logistics & production
Demand and lead-time safety stock Calculator
Estimate buffer stock under uncertain daily demand and replenishment time. This free demand and lead-time safety stock calculator shows the calculation and its assumptions so you can compare your own figures.
Your results
Estimate buffer stock under uncertain daily demand and replenishment time.
Calculated outcomes
- Demand During Lead Time
- 400
- Demand Uncertainty
- 83.9047
Assumptions and estimates
- Independent daily demand and lead-time variation with a normal approximation. Z ≈ 1.282/1.645/2.326 represents 90%/95%/99% cycle service, not fill rate; intermittent or correlated demand needs another model.
- Method: Safety stock = Z × square root of (lead time × daily demand variance + daily demand² × lead-time variance).
- Assumes independent demand and lead-time variation and a normal approximation. Cycle service is not fill rate.
Useful next steps
- Use Compare options to test an alternative side by side.
- Copy, print or download a record of this calculation when you need one.
Reports open your email app addressed to s@s1.ie with the public page address only. Your inputs are never added.
How the demand and lead-time safety stock calculation works
Safety stock = Z × square root of (lead time × daily demand variance + daily demand² × lead-time variance).
Assumes independent demand and lead-time variation and a normal approximation. Cycle service is not fill rate.
Using this calculator
- Enter your own figures in the labelled inputs. Keep the currencies, units and time periods consistent.
- Choose any applicable rate profile, pattern or assumption shown for this tool. Open additional inputs when relevant.
- Review safety stock and reorder point, then read the stated assumptions and eligibility conditions before using the result.
Worked example
This is a static example using illustrative inputs, not facts about you or today’s date. The displayed eligibility selections and assumptions apply only to this example.
See example inputs
- Average daily demand units
- 40
- Daily demand standard deviation
- 8
- Average lead time (days)
- 10
- Lead-time standard deviation (days)
- 2
- Cycle-service normal Z value
- 1.645
- Safety Stock
- 139
- Reorder Point
- 539