Fixed Period Quantity

A fixed-period quantity system, also called a periodic review system, reviews inventory at predetermined time intervals and orders a variable quantity to bring stock up to a target level. The review period is fixed, not the order quantity; replenishment is time-triggered rather than triggered by a reorder point. It accounts for on-hand stock, open orders, and backorders.

In a manufacturing plant using fixed-period control, inventory is counted on a scheduled date, often weekly or monthly. The planner reviews a commodity or SKU group, checks current inventory position, and orders only what is needed to reach a target level that covers demand over the next review interval plus supplier lead time. This is common for raw materials consumed across multiple work centers, because a single review calendar reduces the burden of continuous transaction-by-transaction monitoring. In warehousing, it supports consolidated ordering for many SKUs on the same date, lowering administrative effort and enabling combined shipments. However, the system depends on accurate on-hand balances at review time. If receiving, scrap, backflush, or issue transactions are not current, the computed order quantity is wrong, causing under-ordering or over-ordering. Safety stock is included to absorb demand and lead-time variability, making the model practical for steady-demand items.