E-commerce
September 17, 2026
Are you wondering how to save on your inventory with the EOQ method? The answer is simple: this century-old formula calculates the ideal quantity to order to minimize your total costs, balancing ordering and holding costs. For an e-commerce merchant, it is a direct lever on your cash flow and profitability.
Be careful, EOQ is not a magic wand: it assumes stable demand and ignores seasonal peaks. But properly applied, it avoids costly overstocking and frustrating stockouts. It also helps you negotiate better with your suppliers, because you know exactly what quantity to order to remain profitable.
So, how do you save on your inventory with the EOQ method? On the agenda:
What is the EOQ method and why is it relevant in e-commerce?
How do you calculate ordering cost, demand, and holding cost?
Which formula should you use to find your optimal quantity?
How do you integrate EOQ into your Shopify management?
What are the limitations and alternatives for seasonal sales?
Let's go.
Summary
What is the EOQ method and why use it in e-commerce?
The EOQ (Economic Order Quantity) method was proposed in 1913 by engineer Ford Whitman Harris to help industrial buyers determine the quantity of raw materials to order. Since then, it has expanded to pure players, omnichannel retailers, and DTC brands.
The idea is simple: find the balance point between ordering too often (high ordering costs) and ordering too much at once (high holding costs). In e-commerce, where cash flow is king, mastering this ratio can make the difference between a comfortable margin and unsold stock sitting around. For example, if you order too little, you multiply delivery fees and the time spent managing orders; if you order too much, you tie up money in products that do not sell immediately.
Concretely, the EOQ gives you a precise number of units to order at each replenishment to minimize total cost. It is a steering tool, not a constraint: you adapt it to your reality. It also allows you to better plan your purchases, anticipate needs, and reduce the risks of stockouts or overstocking.
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What are the three costs that make up the total cost of inventory?
Before diving into the formula, it is important to understand that the total cost of your inventory is divided into three components:
Purchase cost: the price paid to the supplier for each unit.
Ordering cost: the expenses associated with placing the order (transportation, time spent, etc.).
Holding cost: everything it costs to store the inventory (rent, insurance, capital tied up).
The EOQ seeks to minimize the sum of these three costs. If you overlook one of them, you risk overstocking or running out of stock. For example, a merchant who only considers the purchase price ignores the hidden costs of warehousing, such as electricity, heating, or management time. By integrating these three components, you get a more realistic view of what your inventory actually costs, and you can make more informed decisions.
How to estimate the ordering cost for your shop?
The ordering cost, also known as setup cost, includes everything necessary to place an order, excluding the price of the goods. This includes freight, the time spent by your purchasing team, any customs duties, etc.
Let’s look at an example: a DTC brand manufacturing in Asia sends a quality engineer on-site for each production run. This trip is part of the ordering cost. On a smaller scale, the time spent by your buyer comparing suppliers, entering the order, and arranging delivery must be valued. Also, do not forget communication fees, potential bank transaction costs, and the time spent receiving and inspecting the goods.
To keep things simple, set a flat rate cost per order. In our example, let's say €100. This figure will be used in the EOQ formula. If you have multiple suppliers, calculate an average cost or perform a calculation per supplier for greater accuracy.
How to define the annual demand for the EOQ calculation?
Demand in the EOQ equation corresponds to the number of units you plan to sell over a given period, typically a year. It is an estimate, not a certainty.
Be careful, the EOQ does not handle seasonal peaks. If your sales skyrocket at Christmas or in the summer, the smoothed annual demand will be distorted. In this case, you can adjust the period: calculate the EOQ over a quarter or a semester, depending on your business. For example, if you sell swimwear, you can calculate the EOQ over the peak period (April to August) to avoid overstocking in winter.
For our example, let's assume a demand of 10,000 units per year. This figure must be realistic, based on your sales history and forecasts. Use your past data, market trends, and upcoming promotions to refine this estimate.
How to calculate the cost of ownership per unit?
The holding cost, or carrying cost, represents the cost of storing one unit over a period. It is often expressed as a percentage of the inventory value, but for the EOQ, an amount per unit is required.
To obtain this, add up the capital, storage, service, and risk costs, then divide by the total inventory value and multiply by 100. Next, multiply this percentage by the unit cost of the product. For example, if your holding cost is 20% and your product costs €10, the holding cost per unit is €2.
This figure is crucial for what follows, as it directly influences the optimal order quantity. A high holding cost will encourage you to order less frequently, while a low cost will allow you to order in larger quantities. Take the time to accurately estimate this cost, as an error can distort the entire calculation.
What are the components of the cost of ownership that should not be forgotten?
The cost of ownership is not just a simple rent. It is divided into four categories:
Cost of capital: the money tied up in inventory could have been invested elsewhere. If you borrow, interest also counts.
Storage cost: rent, utilities, warehouse depreciation, share of overheads.
Service cost: insurance, management software, dedicated labor.
Risk: shrinkage, expiration, obsolescence, theft.
By adding up these items, you get the "total cost of ownership". Divide it by the value of the inventory to get the percentage, then multiply by the unit cost. For example, if your inventory is worth €100,000 and your total costs of ownership are €20,000, the percentage is 20%. If a product costs €10, the cost of ownership per unit is €2. Do not forget to include losses due to unsold or damaged products, as they are part of the risk.
What is the EOQ formula and how do you apply it in a spreadsheet?
Once you have the ordering cost (S), the annual demand (D), and the holding cost per unit (H), the EOQ formula is:
Q* = square root of (2 × S × D) / H
In Google Sheets or Excel, this is written as: =SQRT((2*B3*B4)/B8) where B3 is the ordering cost, B4 is the demand, and B8 is the holding cost per unit.
With our figures (S=100, D=10,000, H=2), the EOQ is 1,000 units. This means you should order 1,000 pieces each time, which is 10 orders per year. It is not an exact science, but a guide to optimizing your purchasing. You can also use online tools or applications to automate this calculation, but a simple spreadsheet is enough to get started.
How to interpret the EOQ result for your purchasing decisions?
The EOQ gives you an optimal quantity to order, but it is not an end in itself. Use it to adjust your replenishment frequencies and supplier negotiations.
If your EOQ is 1,000 units, ordering 2,000 at once increases your carrying costs. Ordering 500 increases your ordering costs. The EOQ helps you find the right balance. For example, if you order 1,000 units, you place 10 orders per year, resulting in a total ordering cost of €1,000 (10 × €100) and a carrying cost of €1,000 (1,000 × €2 / 2). The total cost is therefore €2,000, which is the minimum.
Keep in mind that the EOQ assumes a constant demand. For stable products, it is an excellent tool. For seasonal products, adapt the calculation period or combine it with other methods, such as safety stock or sales forecasting.
What are the limitations of the EOQ for an e-commerce business?
The EOQ was designed for the manufacturing industry, not for e-commerce. Its main limitations:
Non-linear demand: online sales fluctuate with promotions, trends, and seasons.
Variable ordering costs: shipping fees change, as do supplier discounts.
Lead times: the EOQ does not take delivery times into account, which are nevertheless crucial.
Despite these limitations, the EOQ remains an excellent starting point for structuring your purchasing. Combine it with tracking your actual sales to fine-tune. For example, if you notice that your sales increase at the end of the month, you can adjust your orders accordingly. The EOQ is one tool among others, to be used with discernment.
How to integrate EOQ into your Shopify management?
To apply EOQ in Shopify, start by exporting your sales and inventory data. Use a spreadsheet to calculate the EOQ per product, then adjust your reorder points in the admin.
Shopify does not calculate EOQ automatically, but you can create manual restock alerts or use apps. The important thing is to centralize your data to avoid errors. For example, you can set up notifications when stock reaches a certain threshold, based on your EOQ.
To go further, check out our complete guide to managing inventory in the Shopify admin and learn how to integrate Shopify with Amazon to sync your inventory. These resources will help you set up a more efficient replenishment process.
How does Qstomy help optimize your inventory and sales?
Qstomy, the Shopify AI agent, does not calculate EOQ, but it helps you reduce inventory-related costs by improving conversion and decreasing returns. Thanks to its personalized recommendations, it guides your customers to the right products, which increases conversion rates and reduces cart abandonment.
In case of an out-of-stock situation, Qstomy can suggest alternatives or inform customers about restock dates, as explained in our article on managing out-of-stock products seen on an influencer's page. It also facilitates package tracking and customer service, which reduces repetitive requests and frees up your time for purchasing.
Finally, by analyzing the reasons for returns, Qstomy helps you identify recurring issues, such as sizing errors, and correct them at the source. Learn how in our article on analyzing the reasons for returns. By reducing returns, you also decrease inventory and logistics costs, which nicely complements the EOQ approach.
What checklist should you use before applying the EOQ to your inventory?
Before getting started, check these points:
Collect your data: annual sales, ordering costs, carrying costs.
Segment your products: EOQ works best on SKUs with stable demand.
Test on a sample: compare the EOQ with your current orders over 3 months.
Review regularly: costs and demand evolve, adjust your parameters.
In short: EOQ is a powerful tool to reduce your inventory costs, provided you adapt it to your e-commerce reality. Start with one product, measure the impact, then generalize.
FAQ: Is EOQ suitable for small shops?
Yes, even with a small catalog, EOQ helps prevent overstocking. Start with your best sellers.
FAQ: What if my demand is highly seasonal?
Calculate the EOQ for the peak period, or use more detailed forecasts. EOQ remains a guide, not an absolute truth.
To go further: E-commerce product assistant: helping undecided customers choose without pressure - Qstomy, Training an e-commerce chatbot with Shopify: using the right data without creating bad responses - Qstomy, How to use an AI chatbot for product recalls: informing customers without panicking them? - Qstomy.
Enzo
September 17, 2026
