What is safety stock and how much do you need?
Safety stock explained: why it exists, the simple and statistical ways to calculate it, and common mistakes.
Updated 15 October 2026
Why safety stock exists
Demand spikes and late deliveries happen. Safety stock is the buffer that keeps you selling and producing while they do.
The simple method
Safety stock = (maximum daily usage × maximum lead time) − (average daily usage × average lead time). Easy to calculate, but often too generous.
The statistical method
Multiply a service-level factor (1.65 for 95%) by the variability of demand over the lead time. It gives a tighter buffer based on how much your numbers actually move.
Common mistakes
Using one buffer for every item, never recalculating, and forgetting that suppliers' lead times change over time.
Try it with your own numbers:
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