How to Calculate Buffer Stock: Formula + 3 Methods [2026]

Wondering how to calculate buffer stock for your ecommerce business? The buffer stock formula — also called the safety stock formula — sets exactly how much extra inventory to hold as a hedge against stockouts. The most widely used method is (Maximum Daily Sales × Maximum Lead Time) − (Average Daily Sales × Average Lead Time), but it isn’t the right fit for every seller. This guide walks through three proven buffer stock formulas — basic, time-based, and statistical — each with a worked example so you can pick the method that matches your data and set the right buffer level without tying up excess capital.