How do I calculate safety stock for Amazon FBA?
Safety stock = Z-score x demand standard deviation x sqrt(lead time in days). For a 95% service level, Z is about 1.65. Use daily sales variability over the last 90 days. Fewer than 30 days of history means guess higher because variability is under-measured.
Jul 26, 2026 · 3 min read
The formula in practice
Compute daily demand's standard deviation. Multiply by sqrt(lead-time days). Multiply by a Z-score for your service level: 1.28 for 90%, 1.65 for 95%, 2.33 for 99%. That is your safety stock buffer above expected demand during lead time.
Safety stock only holds if lead times and velocity are tracked together, which is what Nova's inventory screen does.
A shortcut that works
For most private-label SKUs a fast approximation is 30% of lead-time demand as safety stock. Refine per SKU where volatility justifies more precision.
Frequently asked questions
Is more safety stock always safer?
No. It buys inventory-driven fees and cash tied up. Match the service level to the SKU's margin.
Do I need different safety stock for seasonal SKUs?
Yes. Compute daily variability inside the season window, not annualized.
What service level should I aim for?
95% is a common default. Hero SKUs may deserve 99%; slow movers may accept 90%.
See this in Nova
Nova surfaces this metric per SKU so you can act before your next monthly close catches it.
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