What a 10% Discount Really Costs Your Margin
- The arithmetic on one product
- What it does to profit, not just contribution
- The general formula
- A table to keep next to the promotion plan
- Use contribution margin, not gross margin
- When a discount is still the right call
- Better alternatives to a straight price cut
- Where this fits
A discount comes straight out of margin, not out of revenue. On a product with a 40% contribution margin, a 10% discount removes a quarter of the money each sale contributes, and you need to sell a third more units just to earn the same total as before.
Most owners feel the discount as 10%. The business feels it as 25% less contribution per sale. That gap is why promotions that “did well on sales” so often leave the month’s profit flat or worse.
The arithmetic on one product
A product sells for ₹1,000. Everything that rises and falls with each sale, including purchase cost, packaging, payment gateway fees and delivery, adds up to ₹600. The contribution per unit is ₹400, a contribution margin of 40%.
Offer 10% off. The price falls to ₹900. The variable cost does not move: the supplier, the courier and the gateway still charge ₹600. Contribution falls to ₹300.
| Full price | 10% discount | |
|---|---|---|
| Price | ₹1,000 | ₹900 |
| Variable cost | ₹600 | ₹600 |
| Contribution per unit | ₹400 | ₹300 |
| Units needed for ₹4,00,000 contribution | 1,000 | 1,334 |
To earn the same ₹4,00,000 of contribution you now need 4,00,000 ÷ 300 = 1,333.3 units, so 1,334 in practice. That is a 33% increase in volume to stand still.
What it does to profit, not just contribution
Suppose this business has fixed costs of ₹3,00,000 a month: rent, salaries, software, the things that do not change with each order.
- At full price and 1,000 units: 4,00,000 − 3,00,000 = ₹1,00,000 profit.
- At 10% off and the same 1,000 units: 3,00,000 − 3,00,000 = zero.
- At 10% off and 1,334 units: 4,00,200 − 3,00,000 = ₹1,00,200, back where you started.
A 10% discount that does not lift volume by a third has not reduced profit by 10%. In this business it has removed all of it.
The general formula
If m is the contribution margin before the discount and d is the discount, both as fractions of the original price:
Required volume increase = d ÷ (m − d)
For the example: 0.10 ÷ (0.40 − 0.10) = 0.333, or 33.3%.
The denominator is what bites. As the discount approaches the margin, the required volume heads towards infinity, and once the discount exceeds the margin, every extra sale loses money and no volume can fix it.
A table to keep next to the promotion plan
| Contribution margin | 5% off | 10% off | 15% off | 20% off |
|---|---|---|---|---|
| 20% | +33% | +100% | +300% | No volume is enough |
| 30% | +20% | +50% | +100% | +200% |
| 40% | +14% | +33% | +60% | +100% |
| 50% | +11% | +25% | +43% | +67% |
Read across your own margin row. A trader running 20% contribution who offers 10% off needs to double volume to stay level. A software or service business at 50% can absorb the same discount with a quarter more sales.
Use contribution margin, not gross margin
The formula only works if m includes every cost that moves with the sale. Gross margin from the profit and loss account usually excludes payment fees, delivery, marketplace commission and sales incentives, all of which scale with each order.
A marketplace seller whose gross margin is 35% may have a contribution margin nearer 20% once commission and shipping are counted. Plug in 35% and the table says a 10% discount needs 40% more volume. The true answer, at 20%, is 100%. The wrong input understates the problem by more than half.
Watch percentage-based costs too. Gateway fees and commissions charged as a percentage of the selling price do fall slightly when you discount, which helps a little. Courier charges, packaging and purchase cost do not.
When a discount is still the right call
None of this means never discount. It means knowing what you are buying with it.
- Clearing stock that would otherwise be written off. If the alternative is selling at scrap value, the relevant cost is what you would recover, not what you paid. A discount that recovers more than scrap is a gain.
- Winning a customer who will buy again at full price. Then the discount is an acquisition cost and belongs in that calculation, spread over the orders it wins, not charged against the first sale alone.
- Filling capacity that is already paid for. A hotel room or a training seat that goes empty earns nothing. Any price above the variable cost adds contribution, provided it does not teach full-price customers to wait for the offer.
- Early payment. A discount for paying upfront is a financing decision. Compare it with what that cash is worth to you, usually the interest rate on your working capital borrowing.
The last condition in the third point is the dangerous one. Regular customers who learn that every month ends in a sale stop buying on the other twenty-five days, and the volume uplift you measured is mostly timing.
Better alternatives to a straight price cut
A bundle, a free add-on with a low variable cost, or free shipping above an order value can deliver the same perceived saving at a fraction of the margin cost. A ₹100 accessory that costs you ₹25 feels like ₹100 to the customer and costs you ₹25, where a ₹100 discount costs the full ₹100.
Where this fits
- The two ratios people confuse: profit margin vs markup
- How many units cover your fixed costs: break-even analysis
- Check the numbers: discount calculator · markup and margin converter · profit margin calculator
- Setting the price in the first place: how to price a service business