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. To evaluate connected inventory signals and purchasing in LineNow, use your own data and check core and add-on terms.