Discount Break-Even Calculator

Discount break-even is the extra sales volume needed after a price reduction so that total contribution (price minus variable cost, multiplied by units) stays the same as before. It compares the contribution per unit before and after the discount. Founders, sales managers and e-commerce teams use it to judge whether a promotion or a negotiated reduction is realistic: if the volume it requires is far above what the discount can plausibly bring, the discount destroys value instead of creating it.

The unit contribution before the discount is the original price minus the variable cost per unit. The discounted price is the original price × (1 − discount ÷ 100), and the unit contribution after the discount is that price minus the same variable cost. Both are currency amounts per unit.

Dividing the old contribution by the new one gives the required volume multiplier: how many units you must sell after the discount for each unit sold before. Subtract 1 and multiply by 100 to read it as the additional volume needed in percent. If you enter current unit sales, the calculator multiplies them by the multiplier and rounds up to a whole unit.

The result depends on the contribution margin, not on gross margin: only costs that change with each unit sold belong in the variable cost. Fixed costs are assumed unchanged, so restoring total contribution also restores the same profit level, no more.

What each term means

Original unit price

Unit price before discount.

Where to find it: The unit price before the discount, excluding VAT or sales tax. Use the price customers actually pay today, after any existing standard discount.

Discount percent

Percent reduction applied to the original sale price.

Where to find it: The reduction you are considering, from 0 to 100. Enter 10 for 10 %.

Variable cost per unit

Costs that change with each sale, such as fulfillment and transaction fees.

Where to find it: Costs that increase with each unit sold: purchase or production cost, packaging, shipping you pay, payment and marketplace fees, sales commissions. Exclude rent, salaries and other fixed costs. Must be lower than the original price.

Current unit sales

Units sold in baseline period before the price change.

Where to find it: Optional. Units sold over a reference period at the original price, for example last month. Gives the required units and the extra units after the discount.

Contribution before discount

Original price minus variable cost per unit.

Contribution after discount

Discounted price minus variable cost per unit.

Required volume multiplier

Old unit contribution ÷ new unit contribution.

Additional sales volume needed (%)

Extra units needed to match previous total contribution, assuming stable variable cost and demand equivalence.

Hypothetical example: a product sells for 100 (excluding taxes) with a variable cost of 60 per unit, and you consider a 10 % discount. Last month, 300 units were sold.

1. Price after discount100 × (1 − 10%) = 90
2. Contribution before discount100 − 60 = 40
3. Contribution after discount90 − 60 = 30
4. Required volume multiplier40 ÷ 30 = 1.33×
5. Additional sales volume needed (%)(1.33× − 1) × 100 = 33.33%

Additional sales volume needed (%) = 33.33%

Contribution per unit falls from 100 − 60 = 40 to 90 − 60 = 30. 40 ÷ 30 ≈ 1.3333, so you need about 33.33 % more units: 300 × 1.3333 = 400 units, 100 more than today, to keep the same total contribution (300 × 40 = 400 × 30 = 12,000). At a 20 % discount, contribution would drop to 20 and volume would have to double (+100 %); at 30 %, contribution would be 10 and you would need four times the volume (+300 %). With a variable cost of 50 instead of 60, the same 10 % discount would need 25 % more units.

Hypothetical numbers, used to show the calculation. Not real company data.

Use this calculator before launching a promotion, a seasonal sale or a permanent price reduction, and before agreeing to a large negotiated discount on the promise of more volume. It turns a vague expectation (“the discount will bring more sales”) into a precise target that can be checked against past results.

It is also a good companion to the sales discount calculator: that one shows what a discount costs per unit, this one shows how much extra volume must make up for it. Together, they help decide whether a discount should be smaller, targeted to fewer products, or replaced by another commercial argument.

Run it per product or product family. A discount that is easily recovered on a high-contribution product can be impossible to recover on a low-contribution one.

The discount is a percentage of the price, but it is paid entirely out of the contribution, which is only part of the price. In the example, a 10 % price cut removes 10 from a contribution of 40: each unit now contributes 25 % less, so you need a third more units to earn the same total.

The relationship is not linear. As the discount approaches the contribution margin ratio (40 % in the example), the contribution per unit approaches zero and the required volume explodes: +33.33 % at 10 %, +100 % at 20 %, +300 % at 30 %. At 40 % the discounted price equals the variable cost and no volume can restore contribution. The curve on this page shows that acceleration for your own price and cost.

Extra volume is not free either. Selling a third more units can require more stock, more working capital, more customer service and sometimes more fixed capacity. And part of the extra sales may be customers who would have bought anyway at full price. The calculator gives the minimum volume under ideal assumptions; reality usually demands more.

The additional volume percentage is the growth in unit sales the discount must produce just to break even on total contribution. Compare it with the uplift you have actually observed in past promotions on similar products.

If the result is shown as not applicable because the discount is too deep, the discounted price is at or below the variable cost: every additional unit loses money and no volume can compensate.

Practical levers

• Lower the discount: on the curve, a few points less can cut the required volume sharply.
• Target the discount to products with a high contribution per unit rather than applying it across the range.
• Reduce variable costs that the promotion adds, such as free shipping or extra payment fees.
• Limit the discount to new customers or larger orders, so that existing full-price sales are not discounted.
• Measure the real volume uplift after each promotion and compare it with the requirement.

Common mistakes

• Expecting a 10 % discount to be compensated by 10 % more sales.
• Using gross margin cost when the promotion also adds shipping, fees or commissions per unit.
• Counting all sales during the promotion as extra, including those that would have happened anyway.
• Ignoring that more volume may require additional fixed costs, such as staff or storage.
• Entering a price including VAT with a variable cost excluding VAT.

Scenario comparison

The conservative case deepens the discount by 5 percentage points and raises the variable cost by 5 %; the optimistic case reduces the discount by 5 points and the variable cost by 5 %. With the example, the conservative case is a 15 % discount with a cost of 63: contribution falls from 37 to 22 and about 68.18 % more units are needed. The optimistic case is a 5 % discount with a cost of 57: contribution falls from 43 to 38 and about 13.16 % more units are needed.

The spread between these cases shows how sensitive the decision is. If a small change in the discount or the cost moves the required volume from modest to unrealistic, keep the discount at the cautious end.

The calculation assumes the variable cost per unit and the fixed costs stay unchanged, and that all units are sold at the discounted price.

It does not model cannibalisation, stockpiling by customers, the effect on future full-price sales or competitors’ reactions.

It targets the same total contribution, not higher profit. Any additional fixed spending for the promotion (advertising, extra staff) raises the volume needed further.

Prices and costs are assumed to exclude VAT or sales tax.