Safety Stock Days Calculator
Buffer stock from demand and lead time variability.
Enter your values
1.65 = 95% service level
ⓘ Live results
Results
- Safety stock
- 42 units
- Days of extra cover
- 2.6
- Service level factor used
- 1.65
- Lead time
- 10 days
Quick answer
Safety stock scales with demand variability, lead time and the desired service level, using the classic square-root formula.
SS = Z x std dev of demand x sqrt(lead time)
How to use the Safety Stock Days Calculator
- 1Enter your target service level as a Z-score (1.65 for 95%, 2.33 for 99%).
- 2Enter the standard deviation of daily demand.
- 3Enter supplier lead time in days.
Inputs explained
- Service level factor (Z)
- 1.65 = 95% service level
Worked example
Using the values the calculator loads with:
Inputs
- Service level factor (Z)1.65
- Daily demand std deviation8 units
- Lead time10 days
Results
- Safety stock42 units
- Days of extra cover2.6
- Service level factor used1.65
- Lead time10 days
Frequently asked questions
Where do I get demand std deviation?
Calculate it from your last several months of daily sales data.
Higher Z-score means what?
A higher Z-score reduces stockout risk but ties up more cash in inventory.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.