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Join early accessSafety stock
Buffer inventory held to absorb demand spikes and supplier delays.
Safety stock is the extra inventory you keep on hand to avoid stockouts when demand runs hot or a supplier is late. It's built into your reorder point. Too little and you stock out; too much and you tie up cash and storage.
In practice
Safety stock is the buffer that absorbs everything your forecast got wrong — a week where sales run 40% hot, a shipment stuck in customs, a supplier who quoted four weeks and delivered in seven. It exists because both demand and lead times are ranges, not the single numbers a planning spreadsheet pretends they are.
Sizing it is an explicit trade between two costs that are easy to feel differently about. Too little and you stock out, losing the sale and — on marketplaces — the hard-won rank that brought it. Too much and you have cash sitting in a warehouse, with the storage fees and obsolescence risk that come with it. The right buffer is bigger for volatile products and unreliable suppliers, and close to zero for steady lines you can restock in days.
Formula
Safety stock ≈ Avg daily sales × safety days of cover
Example: 20/day × 5 days of cover = 100 units of safety stock.
What a good result depends on
Sized to your demand variability and lead-time reliability.
Common mistakes
- Holding zero safety stock on volatile products.
- Over-buffering slow movers and tying up cash.
Questions people ask
- How much safety stock do I need?
- It scales with how variable your demand and lead times are, and with how badly a stockout hurts. Erratic sales or an unreliable supplier justify a deep buffer; predictable, quickly-replenished products need almost none.
- Isn't safety stock just wasted cash?
- It's insurance with a real premium. The question isn't whether it costs money — it does — but whether the cost is less than the lost sales, lost rank and expedited freight it prevents.
- How does it relate to the reorder point?
- Safety stock is a component of it. Your reorder point is expected sales during the lead time plus safety stock, so the buffer is what's meant to be left when a late delivery finally arrives.