Free inventory planning tool
Safety Stock Calculator
Estimate the buffer inventory needed to absorb demand spikes and supplier lead-time changes, then calculate a practical reorder point.
Simple safety stock
Peak-use methodEnter demand and lead-time ranges
Demand
Supplier lead time
Inventory economics
Simple methodSafety stock = (maximum daily demand × maximum lead time) − (average daily demand × average lead time). Reorder point = average lead-time demand + safety stock. If peak assumptions are below the averages, the calculated buffer is shown as zero rather than negative inventory.
Advanced safety stock
Continuous-review modelModel statistical demand and lead-time uncertainty
Demand profile
Lead-time profile
Service & review policy
Inventory economics
Advanced methodThe model combines demand and lead-time variability under an independence assumption. Variability during the protection period is estimated from demand variance across average lead/review time plus the effect of lead-time variance on average demand. Safety stock = service-level z-score × protection-period standard deviation.
Service-level sensitivity
Same demand and lead-time variabilitySafety stock at different service targets
| Service level | Z-score | Safety stock | Trigger inventory | Safety-stock value | Annual holding cost |
|---|
Demand-volatility sensitivity
Service target and lead-time assumptions held constantBuffer requirement as demand becomes more variable
| Demand SD change | Daily demand SD | Protection-period SD | Safety stock | Trigger inventory |
|---|
Lead-time sensitivity
Average lead time is unchangedBuffer requirement as lead-time variability changes
| Lead-time SD | Protection-period SD | Safety stock | Trigger inventory | Lead-variance share |
|---|
Scope
Safety stock protects against variability, not every disruption
The statistical model assumes demand and lead-time variation are reasonably represented by the entered averages and standard deviations, and that demand and lead time are independent. Actual stockout risk can differ when demand is intermittent, highly seasonal, correlated with lead time, constrained by minimum order quantities, subject to batch production, or exposed to major supplier shutdowns. Cycle service level is the probability of avoiding a stockout during a replenishment cycle; it is not the same as fill rate.