Safety stock is the extra inventory you keep on hand beyond your expected demand, held as a buffer against two things you cannot fully predict: sudden jumps in orders and delays from your suppliers. It sits between your reorder point and a stockout, giving you room to keep selling while you wait for replenishment. It is one of the main inputs to reorder planning, alongside lead time and average demand.
How it works
Safety stock is calculated, not guessed. A common approach multiplies your desired service level (expressed as a Z-score) by the standard deviation of demand over your lead time. The more variable your demand or the longer and less reliable your lead time, the more safety stock you need to hit the same service level. It feeds directly into your reorder point, which is typically average demand during lead time plus safety stock.
Why it matters
Too little safety stock and you risk stockouts, backorders, and lost sales. Too much and you tie up cash and warehouse space in inventory that sits idle. The goal is a level that protects your service level without over-investing. For B2B sellers this balance is sharper, because a single wholesale order can be large and irregular, so one missed reorder can leave you short for a key account.
Example
Say you sell 100 units a week with a two-week supplier lead time. Expected demand during lead time is 200 units. If demand swings and deliveries slip, you might hold 60 units of safety stock, setting your reorder point at 260.
Where it fits in B2B quoting
Quoting complicates the picture, because outstanding quotes represent demand that has not yet converted. When a buyer accepts a quote, that stock is committed. If you run quotes through Shopify draft orders, accepted quotes draw down real inventory, so tracking open quote volume helps you judge how much buffer to hold. See the B2B quoting glossary for related terms.