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What is the reorder point?
The reorder point, also called the order point or ROP, is the defined stock quantity of an item at which, once reached or fallen below, a replenishment order is triggered automatically. It ensures that enough material remains available during the replenishment lead time to cover ongoing demand without the warehouse running empty. The reorder point is thus the central signal threshold of consumption-driven materials planning, combining lead time, average consumption and a safety buffer into one concrete threshold value.
How do you calculate the reorder point?
The classic formula is: reorder point = (average daily consumption x replenishment lead time in days) + safety stock. The first summand covers the expected consumption during the lead time, while the safety stock absorbs fluctuations in demand and delivery time. With a consumption of 40 units per day, a replenishment lead time of 10 days and a safety stock of 150 units, the resulting reorder point is 40 x 10 + 150 = 550 units. It is important that the replenishment lead time covers not only the supplier's pure delivery time but also internal times for order processing, goods receipt and inspection.
What is the difference between reorder point, safety stock and minimum stock?
The reorder point is the trigger point for an order and is the highest of the three, since it includes the consumption during the replenishment lead time plus the buffer. The safety stock is only one component of it and, as a reserve, absorbs demand peaks and delivery delays. The minimum stock denotes the iron reserve that should not be touched if at all possible, and in practice it is frequently equated with the safety stock. Anyone who mixes up reorder point and minimum stock in master data maintenance risks systematically incorrect order triggering and thus either shortages or unnecessarily tied-up capital.
How is the safety stock for the reorder point determined?
The safety stock can be set as a flat share of the consumption during the lead time; a common rule of thumb is around one third of daily consumption x replenishment lead time. More precise is a statistical derivation based on the desired service level and the variability of demand and lead time; in the simplest case, with a constant lead time, safety stock = Z x standard deviation of demand x square root of the replenishment lead time. The Z-factor rises with the targeted service level and is around 1.65 for a 95 percent and 2.33 for a 99 percent service level. A higher service level lowers the risk of shortages but increases the capital tied up in inventory, which is why the value should be weighed up according to the importance of the item.
Is the reorder point monitored automatically in the ERP system?
Yes, in the ERP system the reorder point is stored per item as a master data field in materials management. Materials planning continuously compares the available stock against this threshold and, when it is undershot, automatically generates a purchase proposal or, for in-house production, a production order. Reputable systems check against the net available stock, which already factors in open purchase orders and reserved quantities, in order to avoid duplicate orders. ERP solutions from various vendors such as SAP, Microsoft Dynamics, Sage or Infor implement this reorder point method under different names but with comparable logic.
Should the reorder point be fixed or dynamic?
With stable, even consumption, a fixed reorder point that is only reviewed periodically is sufficient. With strongly fluctuating or seasonal demand, a dynamic, regularly recalculated value is more accurate, continuously updating the moving average consumption and thus avoiding both shortages and excess stock. An ABC analysis helps to prioritise the maintenance effort: A-items with a high value share justify precise, often dynamic parameterisation, while C-items are usually adequately controlled with flat fixed values. In both cases it remains crucial that the stored consumption and lead time values are kept up to date.
How does the reorder point method differ from the fixed-interval reordering method?
With the reorder point method, an order is placed exactly when the available stock reaches the defined reorder point, so order dates depend on actual consumption and are variable. The fixed-interval reordering method, by contrast, checks stock at fixed time intervals and tops it up to a target level each time, regardless of the current pace of consumption. The reorder point method is therefore well suited to volatile consumption, while the fixed-interval method offers advantages with stable demand and bundled order processing. Consumption-driven reorder point planning is furthermore distinct from demand-driven planning via MRP, which plans requirements ahead from orders and bills of materials.