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The reorder point is the inventory level at which you place a new order with your supplier. When on-hand quantity drops to or below the reorder point, a replenishment order should be triggered, either manually by your purchasing team or automatically by your ERP.
Getting this number right matters because it sits at the intersection of two costs you are always balancing: the cost of carrying too much inventory and the cost of running out.
Set it too high and you are tying up cash in stock you do not need yet. Set it too low and you hit zero before the next order arrives, which in a manufacturing context means a production line waiting on components.
Reorder Point = Average Daily Usage × Lead Time
Where:
Example:
Reorder Point = 60 × 8 = 480 units
When your on-hand inventory hits 480 units, you place the order. By the time it arrives 8 days later, you will have used approximately 480 units and be close to zero.
This formula works when your demand is consistent and your supplier always delivers on time. In practice, neither is true for most manufacturing environments.
The basic formula covers the average case. To protect against demand spikes and late deliveries, safety stock is added to the reorder point.
Reorder Point = (Average Daily Usage × Lead Time) + Safety Stock
Example (continuing from above):
Now when inventory hits 600 units, the order goes out. By the time it arrives, you have used the 480 units of cycle stock and still have 120 units of safety stock remaining as a buffer. If the supplier is a few days late or demand runs higher than average, the buffer covers you.
For how to calculate the right safety stock number, see the companion post: Safety Stock Formula: How to Calculate the Right Buffer for Your Operation.
If your supplier lead times vary significantly, the average lead time understates your true replenishment risk. A supplier who averages 8 days but occasionally runs 13 days will drain your safety stock in those 5 extra days.
The formula that handles lead time variability:
Reorder Point = (d × LT) + (Z × σ_d × √LT)
Where:
This is equivalent to using the safety stock from Formula 3 (Standard Deviation Method) and adding it to the basic reorder point. If you have already calculated your safety stock using this approach, simply add it to the basic formula as shown above.
For operations where both demand and lead time fluctuate meaningfully, use the full combined variability safety stock from Formula 4 and add that to your basic reorder point.
A contract manufacturer supplies electrical assemblies to industrial OEMs. They source a high-velocity connector from a single supplier.
Component data:
Step 1: Basic reorder point (no safety stock):
ROP = 220 × 6 = 1,320 units
Step 2: Safety stock using combined variability formula:
SS = 1.88 × √(6 × 35² + 220² × 1.5²)
= 1.88 × √(6 × 1,225 + 48,400 × 2.25)
= 1.88 × √(7,350 + 108,900)
= 1.88 × √116,250
= 1.88 × 340.9
= 640.9 units (641)
Step 3: Final reorder point:
ROP = 1,320 + 641 = 1,961 units
When inventory drops to 1,961 units, the order goes out. Given the minimum order quantity of 500, the purchasing team would likely order in multiples of 500 (1,500 or 2,000 units depending on their current stock position and upcoming production schedule).
Without safety stock, this component would be set to reorder at 1,320 units, leaving no buffer against a late delivery or a week with higher-than-average demand. At a 97% service level, the variability-adjusted reorder point is sized to cover all but the most extreme combinations of demand spike and late delivery.
If your supplier delivers in 6 days on average but occasionally takes 10, your reorder point based on the average will leave you short in those 10-day scenarios. Either add a safety stock buffer sized for the variability, or use the maximum lead time you have historically observed in your formula.
Reorder points are not a one-time calculation. They need to reflect current demand and current supplier performance. A reorder point set during ERP implementation based on projected demand figures may be significantly wrong two years later if your volumes have grown or a supplier changed their lead times.
Review your reorder points at least once a year. Prioritize the review for your highest-velocity, highest-margin SKUs where a stockout has the largest operational impact.
A high-volume component used in every production run needs a tightly calculated reorder point sized for variability and a meaningful safety stock buffer. A slow-moving spare part with predictable, low-frequency demand can often be managed with a simple fixed-day buffer. Applying the same formula to all 2,000 SKUs in your catalog wastes time and often produces wrong numbers for the items at both extremes.
Use ABC analysis to segment your SKUs. Apply Formula 4 (combined variability) to your A-items, Formula 2 or 3 to B-items, and a simple fixed-day method to C-items.
Your reorder point calculation gives you the quantity at which to trigger an order. It does not tell you how much to order. If your supplier requires a minimum order of 1,000 units but your reorder point calculation calls for a buffer of 400, those are two different numbers that both need to be accounted for in your purchasing logic.
A reorder point in your ERP generates a replenishment signal. That signal only leads to an order if someone acts on it. If your purchasing team has learned to ignore ERP alerts because they fire too often or at wrong levels, the reorder points in the system are not doing their job. Audit how often replenishment signals are being dismissed versus acted on, and recalibrate accordingly.
The process for updating reorder points varies by ERP, but the logic is consistent:
In NetSuite, reorder points and safety stock are set on the Item record under the Purchasing/Inventory tab, at the location level. In Acumatica, they are set on the IN202000 (Inventory Items) screen per warehouse. In Microsoft Dynamics Business Central, the Reorder Point and Safety Stock Qty fields are on the item card.
For teams using a dashboard to monitor inventory, the reorder point values in your ERP should feed the color-coded alerts in your ops dashboard. When on-hand quantity drops below the reorder point, the row turns yellow. When it drops below safety stock, it turns red. See How to Build a Manufacturing Operations Dashboard with Retool for the dashboard build that connects these figures to an actionable interface.
Safety stock and reorder point are two distinct calculations that depend on each other.
Safety stock answers: how much buffer do I need to protect against variability?
Reorder point answers: at what inventory level do I place the next order?
The reorder point always includes the safety stock as a component. If you calculate your safety stock accurately but set your reorder point using only the basic average formula (without adding safety stock), you are planning to use your buffer before the order arrives, which defeats the purpose.
Correct sequence:
Use the Safety Stock Calculator to calculate both your safety stock and your reorder point for any SKU. Enter your demand figures, lead time data, and service level target.
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