What Is the Reorder Point?
The reorder point is the inventory level at which a business needs to place a new purchase order to avoid running out of stock before the next shipment arrives. It's calculated by combining three pieces of data: how much of a product sells or gets used per day, how long the supplier takes to deliver it, and how much extra cushion the business wants to keep for unexpected swings. Once inventory hits that number, it's time to buy; wait longer than that, and the business risks selling a product it no longer has on hand.
For any business that carries physical inventory — from a hardware store to a multi-warehouse distributor — getting the reorder point right is what separates an operation that never runs dry from one that loses sales because it restocked too late.
Reorder Point Formula
The most commonly used formula to calculate the reorder point is:
Reorder point = (average daily demand × lead time in days) + safety stock
Each variable answers a specific question:
- Average daily demand: how many units of that product sell or get used, on average, on a normal day.
- Lead time: how many days pass between placing a purchase order and the product physically arriving at the warehouse.
- Safety stock: extra units kept as a cushion, in case demand spikes unexpectedly or the supplier runs late.
The result is a number of units, not a date or a percentage: once the available inventory hits that figure, the system — or whoever is in charge of purchasing — should trigger the restock order.
How to Calculate the Reorder Point Step by Step
Calculating the reorder point for a given product follows the same process regardless of the type of business:
- Calculate average daily demand. Add up the units sold or used over a recent period (say, the last 90 days) and divide by the number of days in that period.
- Confirm the real lead time with the supplier. Don't use the "ideal" lead time from the contract — use how long the last several deliveries have actually taken, including any recurring delays.
- Define the safety stock. This depends on how variable the product's demand is and how reliable the supplier has been: more variability or a less reliable supplier means a bigger cushion is needed.
- Apply the formula, adding the safety stock to the result of multiplying daily demand by lead time.
- Review the number regularly. The reorder point isn't fixed — it changes whenever demand, the supplier, or the season changes.
Hypothetical example (for illustration only): say a hardware store sells an average of 20 units of a certain type of screw per day, its supplier takes 7 days to deliver a new order, and the store decides to keep a safety stock of 30 units. Applying the formula: (20 × 7) + 30 = 190 units. In this example, that would mean that once the inventory for that screw drops to 190 units, it's time to place the purchase order with the supplier.
Safety Stock: What It Is and How It Relates to the Reorder Point
Safety stock is the extra inventory a business keeps on top of what "normal" demand would require, specifically to absorb two kinds of variability: selling more than expected, or a supplier taking longer than expected to deliver. Without this cushion, any demand spike or shipping delay leaves the business without product, even if the original average-demand calculation was correct.
A common way to estimate it, when historical peaks are known, is to compare the maximum daily demand against the average daily demand, then multiply that difference by the maximum lead time observed (not the average one). The more erratic a product's demand is, or the less consistent a supplier's delivery times are, the larger the safety stock that product needs — even though that also means more capital tied up in inventory.
Minimum Stock, Reorder Point, and Safety Stock: What's the Difference?
These three terms often get used as if they were interchangeable, but each one means something distinct in inventory management:
- Safety stock is the fixed cushion kept to absorb unexpected swings; it's one of the ingredients that goes into the reorder point formula.
- Reorder point is the inventory level that triggers a new purchase; it includes both the expected demand during the lead time and the safety stock.
- Minimum stock is usually treated as the absolute floor inventory should never touch; in many businesses it matches the safety stock, but in others it's a separate number defined as the critical level that triggers an alert or an urgent order if the reorder point wasn't acted on in time.
In practice, the reorder point works as the signal to act, and minimum stock works as the last line of defense before a product actually runs out. A good inventory system should raise a flag before inventory reaches the reorder point, not only once minimum stock has already been hit.
Common Mistakes When Calculating the Reorder Point
These are the most frequent mistakes businesses make when setting a product's reorder point:
- Using an overly optimistic lead time. Relying on the lead time the supplier promises in the contract, instead of how long the last several orders actually took to arrive.
- Not updating average daily demand. Calculating the reorder point once and never revisiting it as demand shifts with seasonality, promotions, or new customers.
- Ignoring seasonality. Applying the same reorder point year-round for products whose demand swings sharply during certain months.
- Using the same safety stock for every product. A fast-moving item with a reliable supplier doesn't need the same cushion as one with erratic demand and an inconsistent supplier.
- Calculating it in a spreadsheet nobody updates. The reorder point stops being useful once it depends on someone manually recalculating it in a spreadsheet every month, instead of the system itself recalculating it from real sales and delivery data.
Why the Reorder Point Changes Over Time
The reorder point isn't a number you calculate once and forget about. It shifts every time one of its three ingredients changes: if demand for a product grows because of more customers or a peak season, if a supplier starts taking longer to deliver, or if the business decides to free up capital tied up in inventory and lowers its safety stock.
That's why the reorder point works best when it's grounded in up-to-date sales data instead of fixed estimates. A business that regularly reviews its sales history and adjusts its reorder points accordingly has a clear edge over one that sets the number once a year and leaves it untouched, no matter what actual demand does.
How Technology Helps Keep the Reorder Point Up to Date
Calculating the reorder point by hand, product by product, is manageable when the catalog has ten items. Once a catalog has hundreds or thousands of SKUs, with different suppliers and different lead times, manually recalculating every reorder point stops being realistic, and the mistakes get expensive: too much inventory in some products, stockouts in others.
An ERP or a custom inventory system can recalculate each product's reorder point automatically, based on actual sales from recent days and each supplier's real lead time, instead of a fixed figure captured once. This matters especially for businesses already applying just-in-time principles, where keeping inventory lean without running short depends directly on the reorder point staying current with fresh data.
At AISDC, we build custom software that connects sales, purchasing, and inventory in a single system, including inventory management modules that calculate the reorder point per product and alert the purchasing team before stock becomes a problem.
Frequently Asked Questions
What's the difference between reorder point and safety stock?
Safety stock is just the extra cushion against unexpected swings; the reorder point is the full number that triggers a purchase, and it already includes that safety stock added to the expected demand during the lead time.
Is the reorder point the same for every product?
No. Each product has its own daily demand, its own supplier, and its own lead time, so each one needs its own reorder point calculated separately.
How often should I recalculate the reorder point?
It depends on how variable the product's demand is, but as a general rule it's worth reviewing whenever sales shift noticeably, the supplier changes, or at least once per season.
What happens if the reorder point is set too low?
The business risks running out of the product before the next order arrives, which translates into lost sales and customers looking for the product elsewhere.
What happens if the reorder point is set too high?
The business ends up buying earlier than necessary, tying up more capital in inventory than needed, and for perishable or seasonal products, it can end up with stock that never sells.
If your business handles multiple products, suppliers, and warehouses, and calculating the reorder point by hand is no longer enough to avoid stockouts or excess inventory, at AISDC we design custom software that automates that calculation using your real sales and purchasing data.