How to use this calculator
- Enter standard deviation of daily unit demand, constant lead time in days, user-selected normal service z-score.
- Choose a display currency, then select Calculate. Results also update after a brief pause while you edit.
- Read the result with the assumptions below. Export details or save a second scenario to compare your choices.
Formula and method
Assumptions and limitations
Assumes independent daily demand and constant lead time. It does not equal a guaranteed fill rate and does not include lead-time variability.
Worked example
With standard deviation of daily unit demand = 5, constant lead time in days = 16, user-selected normal service z-score = 1.645, safety stock in units is approximately 32.9.
What the result means
The service z-score represents a cycle-service probability only under the stated normal independent-demand model.
Common questions
How should I interpret safety stock in units?
The service z-score represents a cycle-service probability only under the stated normal independent-demand model.
What should I check before using this result?
Assumes independent daily demand and constant lead time. It does not equal a guaranteed fill rate and does not include lead-time variability.
Methodology and transparency
Calculation specification reviewed on 2026-10-14. Mathematical implementation is tested against independent reference fixtures. This does not imply review by a licensed financial professional. Read the testing and precision policy.