How it works
Safety stock = z × daily demand standard deviation × √lead-time days, rounded upward.
Input definitions
- Standard deviation of daily unit demand
- Enter the value in the labeled unit.
- Fixed replenishment lead time (days)
- Enter the value in the labeled unit.
- One-sided normal service factor (z)
- Enter the value in the labeled unit.
A worked example
- Standard deviation of daily unit demand
- 10
- Fixed replenishment lead time (days)
- 9
- One-sided normal service factor (z)
- 1.645
Assumptions & limits
Planning model using entered costs and policies, not country-specific law or a forecast. Use one currency and consistent time periods.
Sources & review
Maintained by AnsRio. Methods and examples use automated checks; this does not imply independent professional certification.
Method updated 2026-10-17. Content checked against the stated method and examples. Our verification approach.
Common questions
Does this account for unpredictable supplier lead time?
No. The square-root formula assumes fixed lead time and independent daily demand. Variable lead time, autocorrelation and non-normal demand require a different model.
How does Safety stock with fixed lead time work?
Safety stock = z × daily demand standard deviation × √lead-time days, rounded upward.
What are the limits of Safety stock with fixed lead time?
Planning model using entered costs and policies, not country-specific law or a forecast. Use one currency and consistent time periods.