Reorder Point Calculator
Find the exact inventory level at which you should place a new purchase order to avoid stockouts during supplier lead time. Use it when setting reorder triggers in your ERP or inventory management system.
About this calculator
The reorder point (ROP) is the stock level that triggers a new order so that inventory does not run out before the replenishment arrives. The standard formula is: ROP = (dailyDemand × leadTimeDays × demandVariability) + safetyStock. Daily demand is your average units sold per day. Lead time is the number of days between placing and receiving an order. The demand variability factor (≥ 1.0) inflates expected demand to account for demand spikes—a value of 1.2 means you plan for 20% higher-than-average demand during lead time. Safety stock is additional buffer inventory held as insurance against both demand and supply uncertainty. Setting the ROP correctly prevents both costly stockouts and excess safety stock that ties up working capital.
How to use
A retailer sells an average of 50 units/day of a product. The supplier lead time is 7 days, and past data shows a demand variability factor of 1.15. The company holds 100 units of safety stock. ROP = (50 × 7 × 1.15) + 100 ROP = (350 × 1.15) + 100 ROP = 402.5 + 100 ROP = 502.5 ≈ 503 units When stock falls to 503 units, place a new purchase order. This ensures you cover expected demand during the 7-day lead time plus a buffer for demand spikes, without running out.
Frequently asked questions
What is the difference between reorder point and safety stock?
The reorder point is the inventory level that triggers a new order, while safety stock is the buffer held within that calculation to absorb demand or supply uncertainty. Safety stock is a component of the reorder point, not a separate concept. If demand and lead times were perfectly predictable, your ROP would simply equal daily demand × lead time days. Safety stock adds the extra cushion on top of that baseline. Reducing lead time variability—through better supplier agreements—is one of the most effective ways to lower both safety stock and the overall reorder point.
How do I determine the demand variability factor for my products?
Calculate the standard deviation of daily demand over a representative historical period (90–180 days) and divide it by the mean daily demand to get the coefficient of variation (CV). A CV of 0.15 suggests a variability factor of around 1.15. Alternatively, use a service-level z-score approach: for a 95% service level, z = 1.645, and the safety component is z × σ × √(leadTime). The simple multiplier in this calculator is an approximation suited for quick planning. For high-value SKUs or critical components, a full statistical approach with a defined service level is recommended.
When should I recalculate reorder points for my inventory?
Reorder points should be recalculated whenever there is a significant change in demand patterns, supplier lead times, or your target service level. At minimum, review ROP values quarterly or after seasonal peaks and troughs. If a new product launch or marketing campaign is expected to spike demand by more than 20%, adjust immediately. ERP and inventory management systems like NetSuite, SAP, or Fishbowl can automate recalculation using rolling demand averages. Failing to update ROPs after demand shifts is one of the most common causes of preventable stockouts and overstock situations.