Safety stock vs real demand — getting the buffer right

Every business holding physical inventory faces the same tension: too little safety stock risks a stockout and a lost sale; too much ties up cash in inventory sitting idle. Getting this balance right depends less on intuition than most businesses assume, and more on actually looking at demand variability.

Why gut-feel buffers are usually wrong in one direction

A buffer set by instinct tends to be either uniformly generous — "let's just keep extra of everything" — which quietly ties up working capital, or uniformly thin to save on holding costs, which causes stockouts on exactly the items with the most unpredictable demand. Neither accounts for the fact that different products genuinely have different demand variability, and deserve different buffer sizes.

What a better approach actually looks at

How much a product's demand fluctuates week to week, not just its average volume. A steady, predictable seller needs a thin buffer. A product with volatile, spiky demand needs a larger one, even if its average volume is lower. Setting the same buffer rule across your entire catalogue ignores this difference and gets both ends wrong.

A simple starting point

Rank your products by how unpredictable their weekly demand actually is, not by how much they sell on average. Put your safety stock budget toward the unpredictable end first — that's where a buffer actually prevents stockouts, rather than just sitting as idle cash on your most predictable, easy-to-restock items.