Safety Stock Calculator
ASCM-style statistical safety stock with demand variability, lead-time variability, service level and reorder point.
Inputs
Combined independent demand + lead-time variability.
Inventory policy result
STATISTICALMethodology
ASCM defines safety stock as protection against demand/forecast and supply variability. For independent demand and lead-time variability, this calculator uses the combined standard deviation of lead-time demand, then multiplies by the Z factor for the selected service level. Reorder point = average lead-time demand + safety stock.
How to interpret the result
Safety stock is a protection buffer against uncertainty; it is not the expected quantity consumed during the replenishment lead time. A higher service target, more variable demand or more variable lead time normally increases the required buffer.
Keep units consistent
If demand is measured per day, lead time and lead-time variability must also be expressed in days. Mixing weekly demand with lead time in days is a common spreadsheet error.
When should the value be reviewed?
Review the calculation after a supplier change, transport-mode change, major demand shift, new program, packaging change or material change in delivery reliability.
Important limitation
The calculation depends on the quality of historical data and the statistical assumptions. Validate critical inventory settings against your ERP logic, procurement constraints, minimum order quantities and continuity rules.