How to Calculate Reorder Point: Formula and Practical Example

Running out of inventory can lead to delayed orders, lost sales, and dissatisfied customers. On the other hand, ordering too early may increase storage costs and leave too much capital tied up in stock.

The reorder point, or ROP, helps businesses decide when they should place a new purchase order. In this guide, you will learn how to calculate the reorder point using a simple formula and a practical e-commerce example.

What Is a Reorder Point?

The reorder point is the inventory level at which a business should place a new order to avoid running out of stock before the replenishment arrives.

It answers one important question:

At what inventory level should we order more units?

The reorder point does not tell you how many units to order. It only determines when the order should be placed.

For example, if the reorder point for a product is 260 units, the business should place a replenishment order when its inventory position reaches 260 units.

Reorder Point Formula

The basic reorder point formula is:

Reorder Point = Average Daily Demand × Lead Time

When a business keeps safety stock, the formula becomes:

Reorder Point = (Average Daily Demand × Lead Time) + Safety Stock

The three main elements are:

Average daily demand: The average number of units sold or used each day.

Lead time: The number of days between placing an order and receiving it.

Safety stock: Additional inventory kept to protect the business from unexpected demand or supplier delays.

How to Calculate Average Daily Demand

Average daily demand shows how many units are sold or used during a typical day.

Use this formula:

Average Daily Demand = Total Units Sold ÷ Number of Days

Suppose an online store sold 900 units during the last 30 days:

Average Daily Demand = 900 ÷ 30

Average Daily Demand = 30 units per day

The store’s average daily demand is therefore 30 units.

Make sure that the period used reflects normal demand. A temporary promotion or seasonal event may produce an unrealistic average.

What Is Lead Time?

Lead time is the time between placing a purchase order and receiving inventory that is ready for sale.

For example:

The order is sent to the supplier on Monday.

The products arrive and become available the following Monday.

The lead time is seven days.

Lead time may include:

Supplier processing time.

Production time.

Transportation time.

Customs clearance.

Receiving and inspection.

Time required to make the products available for sale.

Businesses should measure the complete replenishment process instead of considering transportation time alone.

What Is Safety Stock?

Safety stock is additional inventory kept to reduce the risk of stockouts.

It can protect a business against:

Unexpected increases in customer demand.

Supplier delays.

Transportation disruptions.

Receiving problems.

Inaccurate demand forecasts.

Safety stock should not be selected randomly. It should be based on demand variability, supplier reliability, lead-time variability, and the desired service level.

For this introductory example, we will assume that the business has already calculated a safety stock of 50 units.

Practical Reorder Point Example

Consider a small e-commerce business selling reusable water bottles.

The business has the following information:

Variable Value

Average daily demand 30 units

Average lead time 7 days

Safety stock 50 units

Apply the reorder point formula:

Reorder Point = (Average Daily Demand × Lead Time) + Safety Stock

Insert the values:

Reorder Point = (30 × 7) + 50

Calculate the expected demand during lead time:

30 × 7 = 210 units

Add the safety stock:

210 + 50 = 260 units

The reorder point is therefore:

260 units

The business should place a new purchase order when its inventory position reaches 260 units.

Of these 260 units:

210 units cover expected demand during the seven-day lead time.

50 units provide protection against delays or unexpected demand.

Use Inventory Position, Not Only On-Hand Inventory

A common mistake is to compare the reorder point only with the products physically available in the warehouse.

A more accurate calculation uses the inventory position:

Inventory Position =

On-Hand Inventory + On-Order Inventory − Backorders

Suppose the business has:

Inventory component Quantity

On-hand inventory 180 units

Inventory already on order 100 units

Customer backorders 30 units

The inventory position is:

Inventory Position = 180 + 100 − 30

Inventory Position = 250 units

Because the inventory position of 250 units is below the reorder point of 260 units, the product has reached its reorder threshold.

Using inventory position helps prevent unnecessary orders when additional inventory is already on its way.

How to Calculate Reorder Point in Excel

You can create a simple reorder point calculator in Excel or Google Sheets.

Use the following structure:

Cell Information

B2 Average daily demand

B3 Lead time in days

B4 Safety stock

B5 Reorder point

Enter this formula in cell B5:

=(B2*B3)+B4

Using the example values:

B2 = 30

B3 = 7

B4 = 50

Excel will return:

260

You can use the same structure for multiple products by assigning one row to each SKU.

Reorder Point Without Safety Stock

If demand and lead time are highly predictable, a business may use the basic formula without safety stock:

Reorder Point = Average Daily Demand × Lead Time

Using the previous example:

Reorder Point = 30 × 7

Reorder Point = 210 units

However, this approach provides no protection against unexpected demand or delivery delays. For many physical inventory businesses, including an appropriate safety stock is more practical.

Reorder Point vs. Economic Order Quantity

Reorder point and Economic Order Quantity, or EOQ, solve different inventory problems.

Method Question answered

Reorder point When should we place an order?

Economic Order Quantity How many units should we order?

A business may use both methods together:

The reorder point determines when to order.

EOQ helps estimate the appropriate order quantity.

They should not be treated as interchangeable formulas.

Common Reorder Point Mistakes

1. Using inconsistent time units

If demand is measured per day, lead time must also be measured in days. Do not combine weekly demand with lead time expressed in days without converting one of them.

2. Ignoring lead-time variability

A supplier may promise delivery in seven days but regularly take between seven and twelve days. Using only the shortest lead time can produce an unreliable reorder point.

3. Using outdated sales data

Demand can change because of seasonality, promotions, product trends, or business growth. Update the average demand regularly.

4. Ignoring safety stock

A calculation without safety stock assumes that demand and delivery times are completely predictable.

5. Using on-hand inventory only

Existing purchase orders and customer backorders should be considered when determining whether the reorder point has been reached.

6. Applying one reorder point to every product

Different products have different demand patterns, suppliers, lead times, and risks. Calculate the reorder point separately for each important SKU.

How Often Should You Update the Reorder Point?

There is no single review frequency for every business. The reorder point should be reviewed whenever there is a significant change in:

Average demand.

Supplier performance.

Lead time.

Customer behavior.

Seasonal demand.

Transportation conditions.

Business growth.

Fast-moving or seasonal products may require more frequent reviews than products with stable demand.

Frequently Asked Questions

Can the reorder point be zero?

A zero reorder point may occur when inventory can be replenished immediately, but this is uncommon for products with production or transportation lead times.

Is a higher reorder point always better?

No. A higher reorder point can reduce the risk of stockouts, but it may also increase average inventory and storage costs.

Does the reorder point determine the order quantity?

No. The reorder point determines when to order. It does not determine how many units should be ordered.

Should every product have safety stock?

Not necessarily. Safety stock depends on the importance of the product, demand variability, lead-time uncertainty, stockout consequences, and inventory cost.

Can small businesses calculate reorder points in Excel?

Yes. Excel or Google Sheets can be sufficient for a small product catalog. As the number of products and orders grows, inventory management software may become more practical.

Conclusion

The reorder point gives businesses a structured way to decide when inventory should be replenished.

The standard formula is:

Reorder Point =

(Average Daily Demand × Lead Time) + Safety Stock

In our example:

Reorder Point = (30 × 7) + 50

Reorder Point = 260 units

This means the business should place a new order when the product’s inventory position reaches 260 units.

The calculation is simple, but its accuracy depends on the quality of the demand, lead-time, and safety-stock data. Businesses should therefore monitor these variables and update their reorder points when operating conditions change.