Safety stock calculator

Methodology

This is the combined-variability form: safety stock = Z × √( lead time × demand variance + demand² × lead-time variance ). Z is the safety factor for the target cycle service level, taken from the inverse standard-normal distribution. The first term under the root covers demand varying while lead time holds; the second covers lead time itself varying. Demand during lead time = average daily demand × average lead time, and is shown so the safety buffer can be read against it. The model assumes approximately normal, independent demand and lead-time variation and a fixed target service level. It does not model seasonality, trend, correlated supplier failures, lumpy or intermittent demand, or the cost trade-off between holding and stockout. Cycle service level is the probability of not stocking out during a replenishment cycle — it is not the same as fill rate. You supply every input: this site holds no live freight rates, transit times, or duty tables, and never estimates them for you. Results are an orientation model, not a quotation, and not customs, tax, insurance, or financial advice. Confirm duty rates, VAT treatment, and carrier terms with the relevant authority or provider before relying on them.