Why a technical wholesaler takes a €600 discount on an MOQ of 500 units and loses €1,225 on it

The invoice shows a €600 discount

The buyer at a technical wholesaler receives a quotation for a stainless steel coupling. At 100 units the item costs €9.20. At 500 units, the minimum order quantity for the price-break price (an Asian quotation says MOQ, minimum order quantity), it costs €8.00. The business sells 80 a year, and has done for four years in a row. The buyer orders 500. The invoice shows €4,000 instead of €4,600. In the purchasing meeting that is called a €600 saving, 13 percent on the purchase price.

The coupling then sits in the warehouse for 6.25 years. The discount is on one invoice; the costs of that stock are spread over six sets of annual accounts, on lines such as interest, rent, insurance and write-offs. So the two numbers never meet.

A quantity discount is a one-off amount on one invoice. The inventory costs of the extra quantity keep running every year for as long as that extra quantity sits there, and at some point they overtake the one-off amount. Below is where that point lies.

We see this at wholesalers with a broad range, at importers of own-brand products from Asian manufacturers, at traders in semi-finished products who have to buy per length or batch, and at businesses where the buyer is assessed on purchase price variance. The buyer does what he has been asked to do, get a lower price. His brief says nothing about the 6.25-year holding time.

Why the discount beats the costs in the buyer's mind

Harris (1913), reprinted in Operations Research in 1990 (peer reviewed), already wrote that interest on the capital tied up in materials, labour and overhead sets an upper limit on the quantity you can profitably make or buy at once. In the Netherlands his formula for the optimal order quantity is known as the Camp formula (formule van Camp); Nevi (professional source) calls it a classic mathematical calculation of the optimal order quantity. Internationally the same formula is called EOQ, economic order quantity. The formula weighs ordering costs against inventory costs. A quantity discount sets that trade-off aside, because the price itself changes with the quantity.

So why does a buyer give the discount more weight than the costs? Thaler (1999) (peer reviewed) shows that people and households put spending into separate mental accounts, which violates the economic principle that a euro is the same euro everywhere. Thaler describes households. We see the same mechanism in purchasing departments: the discount falls into the "purchasing result" account, the interest into "financial charges", rent into "premises" and the write-off only years later into "inventory movements". Those four accounts are never added up anywhere.

The supplier has its own reason for the quantity discount. Munson and Jackson (2015), a review in the series Foundations and Trends in Technology, Information and Operations Management, note that sellers have given discounts on large orders for hundreds of years, and that the question for the buyer is how much to order when the supplier presents a price break. Munson and Rosenblatt (1998) (peer reviewed) studied 39 companies to find out why suppliers offer quantity discounts, what the price breaks look like, what they do to centralised purchasing and the number of suppliers, and how they relate to just-in-time delivery. The price break is a seller's instrument: we see that the seller uses it to shift stock, and the costs of it, from his warehouse to yours.

The worked example, from invoice to annual accounts

The wholesaler in this worked example has €9 million revenue, 11,000 items in the warehouse and €1.8 million of stock. The stainless steel coupling is one of those items. All amounts below are model figures; the pattern comes from our client work, and the numbers have been chosen to show the mechanism.

First, inventory costs as a percentage of purchase value per year, in English the carrying cost. We build that percentage up per item group from four components, because an average across the whole warehouse hides the slow movers.

Berling (2008) (peer reviewed) describes how inventory costs are traditionally taken as a fixed percentage of product value, on the grounds that capital costs make up the largest part, and uses an activity-based approach to show that the traditional approach leads in some situations to costs more than 15 percent higher. Gurtu (2021) (peer reviewed) reaches the same conclusion for businesses with a broad range: calculate inventory costs per item rather than with an average percentage; in his study that produced a saving of about 3 percent on inventory costs. The 20 percent in this example therefore applies to this item group: small, light, metal, non-perishable. For a group of large plastic parts that take up many pallet spaces it comes out higher.

Then the two purchasing options, calculated per year. Ordering costs, booking and handling an order, are set at €25 per order. Average stock is half the quantity ordered, because the batch runs down evenly from full to empty.

The option with the discount costs €196 a year more. The order of 500 units covers 6.25 years of sales, so over the life of that one order the difference is 6.25 × 196 = €1,225. The €600 discount is already included: €96 a year in lower purchase price, for 6.25 years. The amount on the invoice is correct. It is just that it is offset by €1,225 of costs that never appear on an invoice from this supplier.

For this item, the Camp formula gives an optimal order quantity of 47 units at €9.20 (the square root of 2 × 80 × 25 divided by 1.84) and 50 units at €8.00. The pack size of 100 is already above that, and the price break of 500 is a factor of ten above it.

What happens if the item is dropped from the range after three years

The 6 percent for obsolescence in the table is an expectation: averaged over hundreds of items, some drop out. For a single item it either happens or it does not. Suppose the customer switches to a different coupling after three years. By then 240 units have been sold and 260 remain, which at €8.00 is €2,080 of purchase value. In this worked example the remaining batch fetches 25 percent of purchase value from a stock buyer: €520 back and €1,560 written off, against a €600 discount.

Van Jaarsveld and Dekker (2011) (peer reviewed) show in a study of service parts that the risk of obsolescence can be estimated from the demand data itself, without expert judgement, and that this improves the inventory decision. For trading stock the translation is simple: an item that sold a steady 80 units a year for four years only gives certainty about those four years. The longer the order covers, the greater the chance that demand stops before the stock does.

How to calculate per purchase order in one minute whether the MOQ discount pays off

The proper method is the table above: total annual costs per option, with purchase value, ordering costs, inventory costs and the risk of a write-off, and then choose the lowest. That is the answer to the question Munson and Jackson (2015) put at the centre for the buyer: how much do you order with a price break. For a buyer with forty orders a day that table is too much work, which is why a two-line version follows below.

Rule one: divide the discount in percent by the inventory costs in percent per year. The result is the number of years the extra stock may on average sit longer. In the example: 13 divided by 20 is 0.65 years, about eight months.

Rule two: calculate how much longer the extra stock actually sits. That is the extra quantity divided by two, divided by annual sales. In the example: (500 minus 100) divided by 2, divided by 80, is 2.5 years.

If the result of rule two is greater than that of rule one, the discount costs money. Here 2.5 years is almost four times the 0.65-year threshold. In euros: 400 extra units divided by two, times €8.00, times 20 percent, is €320 of inventory costs a year against €96 of discount a year. The precise calculation from the table gives €308 of extra inventory costs, because the small option is valued at €9.20 and ordering costs are included. For the decision it makes no difference.

The rule works on the back of the quotation. It also works as a column in the purchasing system: discount in percent, inventory cost percentage of the item group, annual sales from sales history, extra quantity from the price break. The result is a number in years per order line, and an order line with more than a year of extra holding time goes past the purchasing manager.

When the price break does pay off

With the same coupling, the same prices and the same percentage, the order of 500 units wins as soon as sales are above about 220 units a year. The batch is then gone within 2.3 years and the discount of €1.40 per unit (€1.20 price plus €0.20 ordering costs) covers the €308 of extra inventory costs. The threshold shifts with the percentage.

The 12 percent belongs to a business that has the space anyway and works without bank credit: the capital component then falls to what the money would have earned elsewhere, and of the space costs only counting and moving remain. That fits the activity-based approach of Berling (2008), which takes the actual costs of the activity. Even then, 80 units a year is well below the threshold of 132.

There are four situations in which the calculation comes out differently from the above. An announced price increase: according to SMM (2026) (trade media), European steel producers have announced increases on hot-rolled steel for the end of 2026, and then the part of the increase you avoid counts as an extra discount on the units you would otherwise have bought after the increase. With nine weeks of sea freight, a larger batch also has a value as safety stock that is not in the table. If a customer has committed to the volume by contract, annual sales are no longer an estimate. And for raw material for your own processing bought per batch, the pack size is the MOQ and there is little to choose. In all four cases the rule stays the same; only the discount or the annual sales in the rule change.

What the warehouse as a whole shows

The business in this example reports 95 days of inventory. That is the average across €1.8 million and 11,000 items, and the average looks healthy. Sorting per item on stock divided by annual sales shows something else: 2,400 items have more than two years of cover, together €540,000. The part of that above twelve months of sales, the surplus that would not have been there without price breaks and minimum quantities, is €420,000 in this worked example. At 20 percent that surplus costs €84,000 in the first year, and it then shrinks slowly, because by definition these are slow movers.

The quantity discounts that produced that surplus amount to €70,000 in this example, one-off, spread over the purchase invoices of recent years. That is how the buyer can show a better purchasing result for three years while the overdraft facility gets fuller every year. How those inventory days feed into the cash conversion cycle is set out in our article on pre-financing imports. What happens to the surplus if it stays put is covered in the article on dead stock.

Calculate this one level lower than you are used to: per item, per purchase order. The warehouse average hides exactly the orders that matter, because a hundred fast items with 30 days of stock make the twenty slow ones with six years of stock invisible in the statistics. Start with the A items by purchase value; that is where the money is, as our piece on the Pareto principle as a risk gauge works out.

How to use the minimum order quantity and the price break to your advantage

Six measures, each with the number from the example or the source it rests on.

Make the two-line rule a mandatory column in the purchasing system and have every order line with more than a year of extra holding time go past the purchasing manager. In the example that was 2.5 years against a threshold of 0.65.

The buyer's assessment covers the purchase price plus the inventory costs of his orders, using the percentage for the item group. This is our experience: as long as the buyer is assessed only on purchase price variance, he chooses the price break, and rightly so given his brief.

Negotiate on quantity, with the price-break price as the starting point. A framework agreement for 500 units a year in call-off deliveries of 100 often gives the same price-break price without the stock; we see that suppliers who hold stock themselves usually agree to this, because their interest in the price break is the certainty of the volume. Munson and Rosenblatt (1998) studied the effect of price breaks on centralised purchasing and on the number of suppliers. A shared order with a fellow wholesaler or through a purchasing group works in the same way.

Build the inventory cost percentage per item group from the four components in the first table, in line with Berling (2008) and Gurtu (2021), and revise it when interest rates move. 12-month Euribor stood at 3.3 percent on 24 September 2026; each percentage point of interest on €1.8 million of stock is €18,000 a year.

Measure the surplus every quarter: per item the stock above twelve months of sales, added up in euros. In the example €420,000. That number belongs next to the purchasing result in the same report, so that Thaler's (1999) mental accounts meet once a quarter.

With an announced price increase: count the increase as extra discount in rule one. An 8 percent increase with a 13 percent discount makes about 21 percent, and 21 divided by 20 is 1.05 years of extra holding time. That is still less than the 2.5 years of the order of 500.

We run calculations like these for clients, so we have an interest in you taking them seriously. For the rule itself you do not need us.

Frequently asked questions about MOQ and quantity discounts

Does it pay to buy more for a quantity discount if I will not sell that stock for years?

Rarely. Divide the discount in percent by your inventory costs in percent per year; that is the number of years the extra stock may on average sit longer. With a 13 percent discount and 20 percent inventory costs that is 0.65 years. If the extra stock sits longer on average, the discount costs money.

How do I calculate whether my supplier's minimum order quantity (MOQ) costs or saves money?

Compare the total annual costs of two options: purchasing, ordering costs, inventory costs on the average stock and the risk of a write-off if demand stops earlier. In the example above, 100 units per order costs €848 a year and 500 units per order €1,044 a year, despite a €600 discount on the invoice.

What percentage of purchase value does inventory cost per year?

That depends on the item and the business. Build it up from capital, space and handling, insurance and shrinkage, and obsolescence. In the example that comes to 20 percent for small metal parts. Berling (2008) finds that the traditional approach with a single fixed percentage leads in some situations to costs more than 15 percent higher, and Gurtu (2021) advises businesses with a broad range to calculate per item.

What is the Camp formula (EOQ) and does it still work if my supplier imposes an MOQ?

The Camp formula, internationally EOQ and originally from Harris (1913), calculates the order quantity at which ordering costs and inventory costs together are lowest: the square root of two times annual sales times ordering costs, divided by the inventory costs per unit per year. With an MOQ or price break, the price changes with the quantity, and then you compare the total annual costs per price break, as in the table in this article.

How long can stock of one item sit before a purchase discount evaporates?

The extra holding time the discount covers is the discount in percent divided by the inventory costs in percent per year. With a 10 percent discount and 20 percent inventory costs, that is half a year of extra average holding time. The total holding time of the batch may therefore be about a year longer than with the small order, because the average stock is half the batch.

How do I negotiate a lower MOQ or a price break without losing the discount?

Ask for the price-break price based on annual volume in call-off deliveries, with a framework agreement as security for the supplier. We see that suppliers who hold stock themselves often agree to this. A shared order with a peer or a purchasing group is the alternative if the supplier sticks to the batch size.

Why is my cash position falling while my buyer says he is buying more cheaply?

Because the discount appears once on the invoice and the extra quantity sits in the warehouse for years. In the example, €70,000 of quantity discounts produces a surplus of €420,000, which costs €84,000 a year and sits in the overdraft facility. The purchasing result and the inventory costs are in different reports, which is why the difference only shows up when the overdraft facility is discussed.

Further reading: Why a technical wholesaler pays €98,000 every year for €396,000 of inventory that has not moved in twelve months, Why an importing wholesaler with €9 million revenue pre-finances almost €3 million and is still overdrawn despite making a profit, Why an importing wholesaler sees a 39 percent margin on an item that delivers 25 percent after freight, import duty and currency and What the ECB rate rise costs a technical wholesaler that lets its customers pay in 52 days.

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