When inventory reaches this number, place the next order. The textbook formula is avg demand × lead time. This calculator adds service-level sizing and handles both demand variance and lead-time variance, so your ROP reflects reality rather than a weekly average.
The reorder point (ROP) is the inventory level that, when reached, triggers the next purchase order. Once you have your EOQ (see the EOQ calculator) and your safety stock (see the Safety Stock calculator), ROP is the final piece: when to fire the trigger.
Two failure modes this calculator addresses:
ROP = (avg daily demand × avg lead time) + Z × √(SDd² × L + D² × SDL²)
where Z is the service-level Z-score, SDd is std dev of daily demand, L is avg lead time, D is avg daily demand, SDL is std dev of lead time. The square root term is the combined variance when both demand and lead time vary.
Once you have ROP and EOQ, the policy is: monitor inventory daily (or per receiving event); when on-hand + on-order − expected sales until receipt falls below ROP, place a new order for Q = EOQ units.