Safety Stock Formula: Calculation and Example

By mise · Updated September 29, 2026

Quick answer: safety stock = (maximum daily usage − average daily usage) × lead time in days. The statistical version is Z × standard deviation of demand × √lead time. Reorder point = average usage × lead time + safety stock.

Safety stock is the cushion. Too much ties up cash; too little and you run out of your best seller on a Saturday.

Example: a bar uses 6 bottles of vodka a day on average and up to 10 on Saturdays; delivery takes 3 days. Safety stock = (10 − 6) × 3 = 12 bottles; reorder point = 6 × 3 + 12 = 30.

Safety stock calculatorMax daily usageAverage daily usageLead time (days)

Safety stock: —

Service-level formula

Safety stock = Z × σ(daily demand) × √(lead time). Z = 1.65 for 95% service, 2.33 for 99%. For a small business, the simple formula is usually enough.

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Keep reading Par level: meaning, formula and calculator Reorder point formula, with and without safety stock ABC Analysis in Inventory: Example and Steps Stockout: Meaning, Cost and How to Prevent It All guides

Frequently asked questions

Is safety stock the same as par?

No. Par (or the reorder point) includes what you use during lead time plus safety stock.

How do I calculate safety stock in Excel?

=(MAX(usage)-AVERAGE(usage))*lead_time, or =1.65*STDEV(usage)*SQRT(lead_time).

How often should I review it?

Each season or when a supplier changes.

How much does mise cost?

A 7-day free trial, then US$33 a month per location (£26 in the UK).