Safety Stock Calculator

Safety stock is the inventory you keep for the days reality disagrees with your forecast. No plan survives contact with a late container or a surprise BSR spike, and the sellers who sleep are the ones who padded for it.

This calculator uses a service-level factor — how often you're willing to risk a stockout. At 90% you'll run dry about one in ten cycles. At 99% you almost never will, but you pay for the cushion in storage and tied-up cash. Most FBA sellers land at 95%, which is the 1.65 factor.

The formula here is deliberately simple: safety stock = z × (max daily sales − average daily sales) × average lead time. It sizes your buffer to the worst demand swing you've actually seen, stretched across the time it takes to get more. The max-minus-avg term captures how ugly your busy days get; the lead time says how long you're exposed.

If your demand is steady, this number stays small — good, don't hoard. If your sales swing hard or your supplier is flaky, it grows, and that's the honest cost of staying in stock.

Don't confuse safety stock with the reorder point. Safety stock is only the buffer piece; the reorder point adds your normal lead-time demand on top. Pair this with the Reorder Point Calculator so the two line up.

One note: a high service level hides a weak supply chain. If you need 99% to avoid stockouts, the cheaper fix is usually a better supplier or shorter lead time, not a warehouse full of buffer.