Safety Stock Calculator

The statistical version is: Safety Stock = Z × σLT, where Z is the service-level factor (1.65 for 95%, 2.05 for 98%) and σLT is the standard deviation of demand over the lead time. It gives a tighter answer when you have clean daily sales history, but it requires calculating standard deviations per item. The max-minus-average method on this page gets most small businesses to a sensible number without a statistics course.

If safety stock regularly exceeds what you sell during an entire lead time, you are probably over-buffered — that inventory costs money to hold and can become dead stock. Watch two signals: items whose stock never comes close to the safety level (reduce it), and items that still hit stockouts (increase it or fix the supplier). Review levels quarterly and after any supplier or demand change.

No. Prioritize A-items — the roughly 20% of items driving 80% of your sales or the ones whose stockout stops a job — and give C-items little or none. Slow-moving, cheap, or easily substituted items often need no buffer at all; a stockout there is an inconvenience, not a crisis. An ABC analysis tells you which items deserve the buffer.

Safety stock is one ingredient of the reorder point: Reorder Point = (average daily usage × average lead time) + safety stock. The first term covers expected demand while you wait for a delivery; safety stock covers the unexpected. This calculator shows the resulting reorder point automatically, and our reorder point calculator works the same formula from the other direction.

Yes — free, no signup, runs in your browser. StockZip publishes it because setting the number is step one; step two is having software watch it. In StockZip you set the reorder point (including your safety stock) per item, and low-stock alerts fire the moment stock crosses it — free for 100 items.