Free safety stock calculator with simple and service-level (advanced) formulas. Enter demand variability, lead-time variability and a target service level — we compute exactly how many units to hold as a buffer.
Results update live as you type.
Safety stock
140.5units
≈ 3.5 days of average sales covered
Formula
Safety stock = Z × √(LT × σD² + D² × σLT²)Reference: Morocco (MAD). Safety stock is unit-based — no currency conversion needed.
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Stockouts are expensive
Every out-of-stock day costs you direct sales, plus wasted ad spend pushing traffic to a sold-out page, plus lost customer trust.
Overstock is also expensive
Holding too much buffer ties up cash, inflates storage fees and risks obsolescence. Safety stock should be just enough.
Service level is the dial
The target service level (e.g. 95%) lets you trade capital efficiency against stockout risk — per SKU, not per warehouse.
How it works
Measure your demand
Pull 30–90 days of sales for the SKU. Compute average daily sales (D) and, if you can, the standard deviation (σD).
Confirm lead time
Get average supplier lead time (LT) and, if possible, historical variability (σLT) — how late it arrives on bad weeks.
Pick a service level
95% is the standard default. Critical SKUs → 99%. Slow-movers → 90%. The higher the service level, the more capital is tied up in stock.
Hold the buffer
Keep the computed safety stock on hand, and combine with lead-time demand to get the reorder point.
Safety stock = Avg daily sales × Buffer daysQuick and dirty. Use this when you don't have reliable historical data on demand or lead-time variability. A common default is 3–7 buffer days; bump it up for unreliable suppliers or volatile categories.
SS = Z × √( LT × σD² + D² × σLT² )Reference
| Service level | Z-score | Stockouts / 20 cycles | Typical use |
|---|---|---|---|
| 90% | 1.28 | ~ 2 | Slow-movers, low margin |
| 95% | 1.65 | ~ 1 | Standard e-commerce SKU |
| 97.5% | 1.96 | ~ 0.5 | Important SKUs |
| 99% | 2.33 | ~ 0.2 | Hero products |
| 99.9% | 3.09 | ~ 0.02 | Pharma, safety, critical |
Localized
Safety stock is unit-based so it doesn't depend on currency — but we ship a localized page per country for consistency.
FAQ
Safety stock calculator — by country