What Is Reorder Point (ROP)?
Why Is Reorder Point Important?
The reorder point solves a timing problem: if you wait until inventory hits zero before placing a replenishment order, you will stock out during the supplier's lead time. The reorder point tells you the exact inventory level at which to act so that the replacement stock arrives just as your existing stock reaches the safety floor.
Getting the reorder point right has a direct financial impact in both directions. Set it too high, and you hold excess inventory between the trigger and the arrival of the replenishment order — tying up capital unnecessarily. Set it too low, and you run out of stock before the order lands, incurring lost sales, emergency freight costs, and customer churn. The reorder point balances these two risks by building lead-time demand and a safety buffer into a single actionable threshold.
Reorder point pairs with EOQ, which answers how much to order. Together they form a complete continuous-review replenishment policy: EOQ sets the order size; the reorder point sets the trigger. Neither is useful without the other.
How Does Reorder Point Work?
The reorder point is calculated in two parts: the expected demand during lead time, and a safety stock buffer to absorb variability in either demand or lead time.
The first term — average daily demand multiplied by lead time — is how much inventory will be consumed on average while the replenishment order is in transit. If a warehouse sells 100 units per day and the supplier takes 5 days to deliver, the lead-time demand is 500 units. You need at least 500 units on hand when you place the order to avoid stocking out under average conditions.
The second term — safety stock — covers the uncertainty around that average. Demand may spike; the supplier may ship late; the two can happen simultaneously. Safety stock absorbs these deviations and maintains a target service level. The larger the variability in demand or lead time, the more safety stock is required, and therefore the higher the reorder point.
For the full derivation of the safety stock component and how it varies with service level, see the reorder point formula guide.
Reorder Point Example
A distributor sells a hardware component with average daily demand of 100 units. The supplier's average lead time is 5 days. The company's inventory planners have calculated a safety stock of 74 units based on demand variability and a 95% target service level.
Enter your daily demand, lead time, and safety stock — get your reorder point instantly.
What Factors Affect Reorder Point?
Four variables directly determine the reorder point. Each must be measured accurately — an error in any one produces a ROP that either over-stocks or under-stocks.
| Factor | Effect on ROP | Common pitfalls |
|---|---|---|
| Average daily demand | Higher demand → higher ROP (linear) | Using annual demand without converting to daily; using peak-season demand year-round |
| Lead time | Longer lead time → higher ROP (linear) | Using vendor's quoted lead time instead of actual observed lead time; ignoring internal processing days |
| Demand variability | Higher variability → higher safety stock → higher ROP | Omitting variability entirely and setting safety stock to zero; using too short a history to measure standard deviation |
| Target service level | Higher service level → higher safety stock → higher ROP | Applying the same service level to all SKUs regardless of criticality or margin |
Lead time is often the most underestimated factor. Companies frequently use the supplier's stated transit time without accounting for internal processing days — the time from when inventory hits the trigger to when the purchase order is actually submitted and confirmed. If internal processing adds one day to a five-day lead time, the effective lead time is six days, and a ROP calculated on five days understates true requirements by 20%.
Common Reorder Point Mistakes
A zero-safety-stock ROP assumes demand and lead time are perfectly predictable. In practice, both vary. Even small variability — a 10% demand spike or a one-day delivery delay — will consume the gap between the ROP trigger and the order's arrival. The result is a stockout before replenishment lands. Unless demand and lead time are provably constant, always include a safety stock component.
Suppliers quote best-case lead times. Actual lead times — measured from PO submission to stock available in your warehouse — almost always exceed the quote once you account for internal processing, carrier delays, receiving, and put-away. Use a rolling average of observed lead times, not the supplier's nominal figure. The difference is often 1–2 days, which at high demand rates represents significant understocking.
Reorder points become stale as demand evolves and suppliers change their lead times. A ROP calculated on last year's demand underestimates future consumption if demand has grown. Commit to reviewing reorder points at least quarterly, and immediately whenever demand, lead time, or service-level targets change materially.
A 99% service level on a low-margin, easily substituted item results in far more safety stock than is economically justified. A 90% service level on a high-margin, hard-to-source critical component exposes you to disproportionate lost-sale cost. Segment your SKUs by margin, criticality, and substitutability, and assign service levels accordingly — then recalculate safety stock and ROP for each tier.
Frequently Asked Questions
What is the difference between reorder point and safety stock?
Safety stock is the buffer inventory held to absorb demand or lead time variability. Reorder point includes safety stock: ROP = (average daily demand × lead time) + safety stock. Safety stock sets the floor; the lead-time demand component determines when to trigger replenishment so that stock arrives before the safety stock is consumed.
What happens if I set my reorder point too low?
A reorder point that is too low means your replenishment order is triggered after inventory has already fallen into the safety stock buffer — or below it. If lead time is variable or demand spikes during the replenishment window, you will stock out before the order arrives. The cost is lost sales, expediting fees, and customer dissatisfaction.
How often should I recalculate my reorder point?
Recalculate whenever any input changes materially — demand rate, supplier lead time, or desired service level. As a baseline, review reorder points quarterly. High-velocity or high-value SKUs warrant monthly review. A 20% shift in average demand or lead time changes ROP proportionally and should trigger an immediate update.
Can I use reorder point without safety stock?
You can set safety stock to zero, which gives ROP = average daily demand × lead time. This is only appropriate when both demand and lead time are highly predictable and consistent. In practice, nearly every real supply chain has some variability, and operating without safety stock means any deviation from the average will result in a stockout before the order arrives.
Is reorder point the same as economic order quantity (EOQ)?
No. Reorder point answers when to order — the inventory level that triggers a new purchase order. EOQ answers how much to order — the quantity that minimizes total ordering and holding cost. Both are needed to define a complete replenishment policy: EOQ sets order size, and reorder point sets the trigger.