Retail & e-commerce
Discount Margin Calculator
What a discount costs in margin, and the volume it would take to absorb it.
The problem
On an item carrying a twenty percent gross margin rate, meaning margin as a share of the ex-VAT selling price, a ten percent discount wipes out half of it. Discounts are granted on the price and paid for out of the margin, at a ratio intuition underestimates every time. The commercial conversation nonetheless keeps running in percentage of price, on a number that looks modest; the scale of the giveaway surfaces at the category review.
Stacked discounts compound rather than add: three lots of ten percent do not make thirty. A discount placed on an already promotional price bites into margin that has already been reduced, which moves break-even volume far faster than the headline rate implies. Both cases widen the gap and are seldom computed; they are handled explicitly here.
Discount Margin Calculator
How to read the result
Input
- Shelf price (ex-VAT, or VAT-inclusive with the VAT rate) and ex-VAT cost price of the item
- Discount considered, as a percentage or an amount
- Up to four successive discounts, in the order they apply, each as a percentage or an amount
- Starting price: list price or an already promotional price
How to read the result
- The extra volume required is the figure to test against commercial realism; the gross margin rate is shown with the coefficient and the markup on cost
- For a stack, the gap to the arithmetic sum is shown outright, with the discount that would wipe out the margin
- On an already promotional price, margin erodes faster than the headline rate suggests
- What the output supports: grant, cap, or refuse with the volume argument in hand
Limits
- Break-even volume is an arithmetic threshold. The tool says neither whether it is reachable on this item, nor over what period.
- Cost price is assumed fixed. Extra volume that unlocks a supplier rebate tier or changes the logistics scheme improves the answer without being captured.
- Nothing is said about neighbouring items. A discount that pulls volume within the same shelf improves the line's result at the category's expense.
- No memory effect is modelled. Repeated, a discount shifts the customer's reference price and makes the return to list price steadily more expensive.
The calculation holds at item level. Deciding a discount across a range means repeating the exercise at category level. An unreadable entry leaves the last valid value in place with a message, and any value brought back to a limit is flagged. Numbers are read according to the language of the page: comma or point in French, point in English, comma in German and Spanish.
In the glossary
A first thirty-minute conversation
The tool gives the order of magnitude. The decision that follows can be discussed in thirty minutes.