The reorder point is the stock level that, once reached, triggers a replenishment order. It answers a single question, when to order, and is made of two bricks: the demand expected during the delivery lead time, and the safety stock that protects against uncertainty. Well set, it makes goods arrive just before a stockout, neither too early nor too late.
Why it matters
The whole difficulty of replenishment lies in the gap between the moment you order and the moment goods arrive. During this lead time, demand keeps drawing on stock. The reorder point is the threshold that, once crossed, says it is time to order so as not to run out before arrival. It turns a vague hunch, there is not much stock left, into a precise, automatable trigger.
Its business value is direct. A reorder point set too low makes the order arrive too late: stockout, lost sales, emergency shipments. Too high, it orders too early, needlessly inflating average stock and tied-up capital. The right level makes goods arrive just before the safety stock is touched, neither waste nor exposure.
It is also the brick that makes replenishment steerable at scale. Once the reorder point is set for each reference, the when-to-order decision takes care of itself, by exception: the system flags the references that have reached it. The planner no longer watches thousands of lines, they handle alerts. The reorder point is the heart of continuous-review policies.
The reorder point is not a constant: it breathes with lead time and demand. A supplier lead time that lengthens, a demand that accelerates, and the threshold must rise, otherwise the order arrives too late. This is the most common mistake: freezing a reorder point computed once, then letting it drift as reality changes.
The expert lesson: watch both ingredients. Consumption during the lead time follows demand; safety stock follows variability. A healthy reorder point is recomputed when lead time or variability move, and it is differentiated by reference: a reference with a long lead time and nervous demand triggers far earlier than a stable one delivered in two days.
The mechanism
The reorder point adds two quantities. The first is the expected consumption during the lead time: how much you will sell, on average, between ordering and receiving. It is the average demand times the lead time. The second is safety stock, the buffer that absorbs demand and lead-time uncertainty over that same window.
The diagram shows the mechanics. Stock declines at the pace of demand. When it reaches the reorder point, an order goes out; during the delivery lead time (light zone), demand keeps pulling it down; on arrival, stock has just reached the safety level, and the delivery lifts it back up. Well calibrated, stock never drops below the buffer, except in exceptional cases.
Everything therefore hinges on measuring lead time and demand. An underestimated lead time, and the threshold is too low: stockout. An underestimated demand, same error. That is why the reorder point is computed on clean data, at the reference level, and revised as soon as either parameter changes durably.
The traps
Computing the reorder point once and forgetting it is the classic error. Lead times and demand drift; a frozen threshold soon becomes too low, hence stockouts, or too high, hence overstock. It is recomputed at the pace its ingredients change.
The trigger must read on the stock position, on hand plus on order minus backorders, not on physical stock alone. Ignoring orders already on the way leads to reordering while a delivery is arriving, and to mechanical overstocking.
The lead time that matters is not the contract one but the real, door-to-door lead time, variability included. Trusting the theoretical, shorter lead time places the threshold too low and guarantees stockouts as soon as the supplier runs late.
The rollout
Estimate average demand and the real lead time at the reference level, on clean history. These are the two inputs of the threshold; a wrong input spoils everything.
Take the buffer computed for the target service level (see Safety stock) and add it to consumption during the lead time. Service is differentiated here, reference by reference.
Trigger the order on the stock position, physical plus in transit minus backorders, not on physical alone, so as not to reorder what is already on the way.
Recompute the threshold as soon as a lead time lengthens or a demand changes durably, and watch stockouts: they signal an under-sized reorder point.
From knowledge to action
Frozen reorder points, computed once then forgotten, are the first cause of avoidable stockouts. Our Inventory & distribution file resets your thresholds on your real lead times and demand, reference by reference.