Free, in-browser. Computes safety stock three ways — demand variability only, lead-time variability only, and the combined formula — so you can see which source of uncertainty is actually costing you the buffer. Nothing leaves your machine.
Demand variability only: SS = z × σ_d × √LT Lead-time variability only: SS = z × d × σ_LT Combined (independent inputs): SS = z × √(LT × σ_d² + d² × σ_LT²)
The combined approximation includes demand and lead-time variability and assumes they are independent. Check that assumption and the normal approximation before using the result. The z-score represents modeled cycle service, not guaranteed fill rate. If lead-time variability dominates, compare supplier reliability improvements with the cost of more inventory. Shortage cost and holding cost help frame that decision.
=AVERAGE(...), =STDEV.S(...)).Review the observed demand pattern and test the planning assumptions for your items. For connected stock signals and purchasing, explore LineNow’s replenishment software. View the core plan and add-on terms.