Discount Break-Even Calculator
How many extra sales a discount must generate before it earns its keep
Updated 2026-09-09
- Margin after the discount
- 30.0%
- Extra unit sales needed
- 33.3%
That is the volume increase needed just to earn the same gross profit as before the discount.
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A 20% discount rarely costs 20%. On a 40% margin it wipes out half your gross profit per sale, so the promotion must double unit sales just to stand still. This calculator shows the volume increase your discount actually demands before you commit to it.
The arithmetic behind a discount
Discounts come off the price, but the cost of the item does not move. On a $100 item with a 40% margin, you keep $40. Discount by 10% and the price drops to $90 while the cost stays at $60 — you now keep $30, a quarter of your gross profit gone on every unit.
To earn the same total gross profit you need 33% more unit sales. The formula is the discount divided by the margin remaining after it, expressed as a percentage.
Why thin margins cannot afford discounts
The required volume climbs steeply as margins fall, which is why grocery-style businesses discount on a few loss leaders rather than across the range.
- 50% margin, 10% off — needs 25% more sales
- 40% margin, 10% off — needs 33% more sales
- 30% margin, 10% off — needs 50% more sales
- 25% margin, 20% off — needs 400% more sales
- Any discount at or above your margin loses money on every unit sold
Alternatives that protect margin
Most discounting is a reflex. These usually move the same volume for less profit given away.
- Bundle a slow item with a fast one at a modest combined saving
- Add value — free delivery, an accessory, an extended guarantee — instead of cutting price
- Offer the discount only on a minimum spend so average order value rises with it
- Time-box the offer so it does not reset customer expectations of your normal price
- Discount clearance stock deeply and current stock rarely, rather than shallow discounts on everything
When a discount is genuinely the right call
Clearing stock that is tying up cash or heading for obsolescence is worth almost any price above cost — the alternative is a total write-off. Acquiring customers who reliably return can also justify a first-order discount, provided lifetime value supports it.
The trap is habitual discounting on healthy stock to hit a monthly number. That trains customers to wait for the sale, and the next full-price week pays for it.
Measuring whether the promotion worked
Compare gross profit, not revenue, against a matched period before the promotion. Revenue almost always rises during a discount; gross profit is the number that tells you whether the extra volume covered the margin you gave away. Track unit sales too, so you can see whether you sold more or simply sold the same units cheaper.
Keep the numbers in a spreadsheet
Ready-made Excel and Google Sheets templates that pick up where this calculator stops. One-off purchase, instant download.
Simple Profit & Loss (P&L) Statement Spreadsheet
Log transactions; get a monthly and yearly P&L with margins.
Frequently asked questions
How do I calculate discount break-even?
Divide the discount percentage by the margin percentage remaining after the discount. A 10% discount on a 40% margin leaves 30%, so 10 ÷ 30 = 33% more unit sales needed.
Why does a small discount cost so much profit?
The discount comes entirely out of your profit, not your cost. On a 40% margin, ten points of discount is a quarter of everything you were keeping.
What discount can I safely offer?
One your margin can absorb with a realistic volume lift. If the required increase looks implausible for your shop, the discount is too deep.
Is a discount better than a bundle?
Usually not. A bundle raises the order value and moves slower stock while giving away less margin per sale.
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