Off-invoice discounts, volume rebates and net-net cost: how to find a product's true purchase cost

What is the difference between the invoice price, an off-invoice discount, a volume rebate and a promotional contribution?

An annual supplier agreement usually carries four kinds of item, and each enters cost at a different time and through a different document. The list price (gross price) is the unit price on the purchase invoice line. An off-invoice discount is deducted on the same invoice, below the line total; it can come in one or several tiers and is known the moment the goods are received.

A volume rebate is also called a year-end rebate or target rebate: a discount granted afterwards, as a percentage of purchases, once a set purchase value or quantity is exceeded within a period. It is not known at delivery; whether the target is met is settled at period end. That is why it does not appear on the purchase invoice and is closed with a separate document.

A promotional and marketing contribution, by contrast, pays for a specific promotion or service: a weekly-offer contribution, a leaflet and in-store announcement, a special position on a display unit. It is not a price discount but an agreement with something given in return, and, as the legal section explains, it is subject to its own rules. That is why it sits on a separate line in the cost calculation.

The names vary from company to company: the same payment is a volume rebate in one agreement and a target rebate or year-end discount in another. What matters for the calculation is not the name but when the item becomes known and what it depends on.

How are net, net-net and triple-net cost calculated?

Each of the three is obtained by deducting one more layer from the previous cost. Net cost is the invoice itself: the off-invoice discounts are deducted from the list price. Net-net cost also deducts the per-unit share of conditional and later discounts, the volume rebate first among them. Triple-net cost then deducts the per-unit share of promotional and marketing contributions.

Tiered discounts are multiplied, not added. Two off-invoice discounts of 8 per cent and 2 per cent make not 10 per cent but 1 − 0.92 × 0.98 = 9.84 per cent; the second discount applies to what is left after the first. If the agreement explicitly says the discounts are added, the calculation follows the agreement.

None of the three numbers is right or wrong on its own; each answers a different question. The problem is a report that does not say which one it uses. Companies also define net-net and triple-net differently, so the definition is written down once inside the company and stated on every margin screen.

Net cost

List price × (1 − Discount 1) × (1 − Discount 2) …

Per-unit volume rebate

Net cost × Rebate rateWhen the rebate is defined on purchase value. If it is defined per unit or as a fixed amount, the total expected rebate is divided by the expected purchase quantity.

Net-net cost

Net cost − Per-unit volume rebate − Per-unit other conditional discounts

Triple-net cost

Net-net cost − (Period's promotional and marketing contributions ÷ Period's purchase quantity)

1. Split the agreement into itemsEach supplier agreement is split into three groups: off-invoice discounts, conditional rebates and contributions paid for a service. The rate, base (value or quantity) and condition of each item are written down.
2. Take net cost from the invoice lineDiscounts already applied on the invoice at goods receipt are net. If the agreement states a discount that does not appear on the invoice, the gap is closed with the supplier at goods receipt, not left for later.
3. Write down the expected outcome of the conditional rebateCompare the annual target with purchases to date. The expectation that the target will be met rests on the purchase plan; it is an assumption and stays labelled as one in the report.
4. Divide the contribution by quantityA promotional contribution is divided either by the units of the promotion period (for promotion profitability) or by annual units (for triple-net). The report header states which one is used.
5. Fix the definitionWhich margin is calculated on which cost is written down once and not changed between periods; otherwise two periods cannot be compared.

Worked example: net-net cost and the margin difference

In the example below, one product's annual agreement carries four items. The figures are illustrative and exclude VAT. The selling price is held constant; the only thing that changes is which cost the margin is calculated on.

The same product at the same shelf price shows three different margins depending on the cost used. The gap looks small, but it repeats on every unit sold and, across a category, grows large enough to change pricing and promotion decisions.

Here the promotional contribution is divided by annual units. When the promotion's own profitability is assessed, the same contribution is divided only by the units sold during the promotion; the two calculations are not mixed in one report.

How does a year-end volume rebate distort monthly margin?

A volume rebate is earned on purchases made throughout the year, but it is often booked in one go at year end, once the target is confirmed. This does not change the annual total; it changes how the months look. Eleven months show a margin that is too low, the last month one that is too high, and month-by-month category comparison loses its meaning.

In management reporting the remedy is accrual: the expected rebate is spread across the months as purchases are made. An accrual is an estimate; in the month it becomes clear that the target will be missed, the accumulated accrual is reversed and the correction is shown on a separate line. When and in which account the statutory entry is made is a separate decision, taken with your accountant.

The second trap is stock on hand. The rebate is calculated on purchases, the margin on sales. The rebate attributable to goods still in the warehouse and on the shelf at period end belongs to goods not yet sold; deducting the whole rebate from the period's cost of goods sold inflates the margin. The rebate is spread over the units purchased; the share of the units sold goes to cost of goods sold, the share of the units still in stock goes to stock value.

Monthly rebate accrual

Month's net purchase value × Expected rebate rateThe expected rate is read from the target tier the annual purchase plan falls into; if the target will not be met the rate is zero and the accumulated accrual is reversed.

Rebate attributable to goods sold

Period's rebate × (Units sold ÷ Units purchased)

• Target missed: the accumulated accrual is reversed in the month it becomes clear; the correction shows on its own line and past months do not change silently
• Goods still in stock: the share of the rebate attributable to stock on hand is not deducted from the period's cost of goods sold
• Tiered rebate: if the purchase plan sits just above a tier, a small deviation changes the rate; the expected tier is stated in the report
• Price floor: if an unconfirmed rebate is fully built into the price floor, margin falls short of plan when the target is missed

What does Turkish retail law say about supplier premiums, promotional contributions and payment terms?

The relationship between supplier and retailer is governed by Law No. 6585 on the Regulation of Retail Trade and the Regulation on Principles and Rules in Retail Trade. Articles 6 and 7 of the Law were amended by Law No. 7435 of 26 January 2023; Articles 4 and 5 of the Regulation were amended on 14 December 2023. The changes came into force on 1 January 2024.

Article 6 of the Law treats certain practices as unfair commercial practices in all cases. Two of them bear directly on premiums and fees: charging fees under names such as store opening and renovation, turnover shortfall, bank and credit card participation fee and others without providing a service that directly affects product demand; and charging premiums and fees without stating in the contract the type of service provided and the amount or rate of the fee. Article 4 of the Regulation gives activities, advertising, magazines, announcements and special positioning on display units as examples of services that directly affect demand, and requires the contract to state, besides the type of service, its duration and/or number.

The same article treats passing the cost of a promotion on to a party that does not wish to run it as an unfair commercial practice. It requires the terms of the commercial relationship in the supply of agricultural and food products to be set in writing; the Regulation accepts, besides a written contract, an agreement shown by email, fax or other written electronic means. Contract clauses that give one party the power to change terms unilaterally to the other's detriment, or that are not clear and understandable on essential points such as payment terms, returns and promotion terms, are on the same list.

Most sanctions are proportional. Under Article 18 of the Law, the administrative fine for breaching the premium and fee rule equals the premium and fee unfairly charged, and for breaching the promotion rule it equals the promotion cost passed on. Breaches of the written contract and contract clarity rules carry a fixed fine per breach; according to the table annexed to the Law, the 2026 amount is ₺57,241.

Payment terms are in Article 7. Payments are, as a rule, made within the term set in the contract; for agricultural and food products there is also a ceiling. For products that can perish within thirty days of production, the term may not exceed thirty days where the creditor is small (micro or small under the Regulation) and the debtor medium or large, or where the creditor is medium and the debtor large, and forty-five days in other cases. For other agricultural and food products, the term may not exceed sixty days in the same size pairings. The term runs from delivery or transfer of ownership, whichever is earlier, and the burden of proving timely payment lies with the debtor.

The practical conclusion for costing: every premium and contribution has a counterpart, type, duration and amount or rate stated in the contract, and the cost entry is tied to that contract line. A contribution with no counterpart in the contract is both an unexplained item in the margin report and a regulatory risk.

This section is general information, not legal advice. How a particular premium or contribution is assessed under Article 6 of the Law depends on the specific terms of the contract; agreements are reviewed against the text in force and with a lawyer.

How are discounts and volume rebates treated for tax and accounting?

On the VAT side, the distinction depends on the document. Under section III/A-6.1 of the VAT General Implementation Communique, a discount shown on the invoice and in line with commercial practice is excluded from the VAT base under Article 25/a of Law No. 3065. Discounts not shown on the invoice and granted at year end, at the end of a set period or once a set turnover is exceeded, under names such as sales premium, turnover premium or year-end discount, change the VAT base of the original transaction and are corrected under Article 35 of the Law.

The Communique also sets out how the correction is made: the buyer issues an invoice or similar document to the seller and applies to the discount amount the VAT rate that applied to the original supply on the date it was made. The chain receiving the volume rebate is the buyer in this relationship, so under the Communique it is the chain that issues the document.

On the accounting side, paragraph 11 of TMS 2 Inventories states that trade discounts, rebates and other similar items are deducted in determining the costs of purchase. This points the same way as the net-net logic in this guide: the rebate reads as a reduction of purchase cost, with the share attributable to goods sold going to cost of goods sold and the share attributable to stock on hand going to stock value. How contributions that pay for a distinct service, such as advertising, are classified is assessed separately.

Which accounting framework applies, and in which account and period the entry is made, depends on the company's accounting policy. The monthly accrual in management reporting and the statutory entry need not fall on the same date; the difference between them shows on a separate line in the report.

This section is general information, not tax or accounting advice. The Communique has been amended since publication; the treatment is set up against the text in force and with your accountant.

Where do product cost and margin appear in Mindpera?

Mind Cost recalculates weighted average cost on every goods receipt; last purchase cost sits in a separate column on the same row, and the gap between them is shown as an amount and a percentage. Gross margin, net margin and post-markdown margin are calculated separately on both cost methods, so every screen makes clear which cost the report uses.

Every cost value can be traced back to the invoice, the date and the calculation step it came from. Cost corrections are not applied silently to the past; they are written as a separate movement type, with the period the correction belongs to and the date it was posted held in two separate fields. When a document arriving at year end is posted as a cost correction, the reason for the difference stays visible line by line even if last month's report is printed again.

If the accounting system and the purchase and expense invoices sit in different sources, our team handles the installation and brings the sources into the same data model.

• Average and last purchase cost on the same row, with the gap as an amount and a percentage
• Gross margin, net margin and post-markdown margin separately on both cost methods
• Cost trail: invoice, date and calculation step
• An alert to the pricing owner when last purchase cost crosses its threshold