Safety Stock Calculator
Find the right buffer to protect against demand and lead-time variability — without overstocking. Enter your numbers, pick a service level, get an instant answer.
How much daily demand fluctuates.
How variable supplier delivery is.
Service level is the % of demand cycles you want to fulfill without stocking out. 95% is a common default.
Safety stock
341 units
Reorder point
1041 units
σ over lead time
207 units
Reorder point = (avg demand × avg lead time) + safety stock. Place a PO when on-hand stock falls to this number.
How safety stock is calculated
Safety stock is extra inventory you hold to protect against the two main sources of stockouts: demand spiking unexpectedly, and suppliers delivering late. The standard formula combines both:
SS = Z × √( LT × σd² + d² × σLT² )
Z is the service-level factor (1.65 for 95%, 2.33 for 99%). LT is your average lead time, σd the standard deviation of daily demand, d average daily demand, and σLT the standard deviation of lead time.
Most teams over-buffer because they pick service levels by gut. Bumping from 95% to 99% can nearly double your safety stock — which is why measuring real demand variability matters.
Frequently asked questions
What service level should I use?+
95% is a sensible default for most SKUs. Critical components or high-margin items justify 99%. Slow-moving items can sit at 90% or lower to free up cash.
Where do I get demand and lead-time standard deviations?+
From your sales and PO history. Pull the last 90 days of daily sales for the SKU and compute the standard deviation. Same for actual vs promised supplier lead times.
What if my demand isn't normally distributed?+
The Z-formula assumes normal-ish demand. For lumpy or seasonal SKUs, look into Croston's method or simulation. Stoccly's insights handles these patterns automatically.
Should I use the same safety stock formula for every SKU?+
No. Segment SKUs by value and criticality (ABC analysis). Use higher service levels and more rigorous formulas for A items, simpler buffers for C items.
How often should I recalculate safety stock?+
At least quarterly, and any time you change suppliers, launch a new product, or notice demand patterns shifting. Stoccly recalculates continuously.
Stop calculating in spreadsheets. Let Stoccly do it.
Stoccly tracks your real consumption, lead times, and demand variability — and turns them into per-warehouse reorder points and stockout forecasts automatically.