Browser-local worksheet
Enter your inputs
Nothing is uploaded or saved
How to use it
A short, reviewable workflow
- 01
Enter at least three observed lead times separated by commas.
- 02
Select a planning service level.
- 03
Review unusual observations and the normal-distribution assumption before adopting the allowance.
Useful for
Common use cases
- Supplier lead-time review
- Planning parameter maintenance
- Quantifying delivery variability
Important boundary
What this result cannot decide
Inspect outliers and disruption modes instead of relying only on the average or a normal approximation; critical items may require scenario analysis.
Model notes
Assumptions and limitations
Assumptions
- Observations are independent and representative.
- A normal approximation is suitable for the selected allowance.
- All observations use the same day basis.
Limitations
- Small or skewed samples can make the allowance misleading.
- Seasonality, demand variability, and disruption scenarios are excluded.
- The calculation is not a guaranteed service level.
Questions
Frequently asked
What does the service level change?
It changes the z-score multiplied by sample standard deviation to estimate a safety-time allowance.
Why use at least three observations?
Sample variability cannot be meaningfully estimated from one value, and two remain extremely fragile.