Safety Stock & Reorder Point Planner

Size your buffers with a classic normal-demand model. Supply the average demand, its variability, lead time, and target service level to instantly obtain the reorder point that protects against stock-outs.

Mean demand for the SKU during each replenishment period.
Standard deviation of demand over the same period.
Replenishment lead time expressed in the same periods as demand.
Desired probability of not stocking out during lead time.

Examples

  • Demand 120 units, σ 35, 10-period lead time, 95% service ⇒ reorder point 1,382.03 units
  • Demand 800 units, σ 120, 4-period lead time, 90% service ⇒ reorder point 3,507.61 units

FAQ

What if demand is not normally distributed?

Use historical percentiles or simulation to estimate a custom Z value, then enter the equivalent service level to mirror those results.

Can I use different units for lead time?

Yes, as long as the demand and lead time share the same period—weeks with weeks or days with days—so the math stays consistent.

How do I factor multiple suppliers?

Model each supplier separately to find individual reorder points, then weight by share of supply or choose the worst-case lead time to stay conservative.

Additional Information

  • Safety stock equals Z × σ × √lead time under the assumption of normally distributed demand.
  • Service level is converted to a Z-score via an inverse error function approximation for speed.
  • Resulting reorder point adds expected demand during lead time plus the calculated safety stock.

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