Inventory reorder point calculator

The reorder point is when to order, not how much: it is the demand you expect to serve during the lead time plus safety stock for the days the world runs late. The working assumes demand and lead time vary independently and roughly normally; a seasonal product invalidates any static reorder point, and periodic review (checking stock on a schedule) needs the review interval added to the lead time. Position here means on hand plus on order minus back orders; if you track back orders, subtract them yourself before entering.