Business calculators
Safety Stock Calculator
Calculate the buffer inventory needed to cover demand and lead-time variability. Your inputs stay in this browser.
Live calculator
Enter your numbers
What this calculator measures
Safety stock is buffer inventory held to cover the gap between expected and worst-case demand and supplier lead time. It protects against stockouts without requiring you to hold enough inventory for the worst case at all times.
This calculator uses the common maximum-minus-average method, which compares your highest plausible daily usage and lead time against your average usage and lead time.
Formula
Inputs and variables
- Maximum daily usage
- Enter the value used by this formula.
- Maximum lead time (days)
- Enter the value used by this formula.
- Average daily usage
- Enter the value used by this formula.
- Average lead time (days)
- Enter the value used by this formula.
How to use the calculator
- Choose a display currency when money fields are present.
- Enter values that cover the same period, scope, and currency.
- Review the result, formula, and worked example before using the estimate in a decision.
- Change one assumption at a time to understand what drives the result.
Worked example
- 1Maximum daily usage is 120 units with a 12-day maximum lead time.
- 2Average daily usage is 100 units with an 8-day average lead time.
- 3Safety stock = (120 x 12) - (100 x 8) = 1,440 - 800 = 640 units.
How to interpret the result
The reorder point — average usage during the average lead time, plus safety stock — tells you the inventory level at which to place a new order.
Common mistakes and limits
- Using unrealistic maximum values that inflate safety stock unnecessarily, ignoring seasonal demand spikes, or never revisiting the inputs as demand patterns change.
Frequently asked questions
What if my maximum usage equals my average usage?
Safety stock will be driven entirely by lead-time variability in that case.
Does this method account for demand forecasting error statistically?
No. This is the simpler max-minus-average method; statistical methods use demand variability and a service level target instead.
Can safety stock be zero?
Yes, if your maximum and average usage and lead times are identical.