Discount Impact Calculator
Quick answer: A discount comes entirely out of your margin: new margin = discounted price − unit cost, and the sales-volume increase needed to keep total profit flat is the original margin divided by the new margin. A $100 item with $60 cost discounted 10% drops per-unit margin from $40 (40%) to $30 (33.3%) — so you must sell 33.3% more units just to break even on profit.
Enter your current price, unit cost, and discount to see the full impact: how much margin you lose in dollars and percentage points, and the exact sales lift required to hold total profit flat. Instant recalculation as you type.
Enter your numbers
Your results
How to use this calculator
Enter your regular selling price, your per-unit cost (materials, wholesale price, or cost of goods sold), and the discount percentage you are considering. The results table updates instantly.
Read the "break-even sales-volume increase" row as your target: if the promotion does not deliver at least that lift, total profit falls even though revenue may rise. Compare this target to the lift you actually achieved after past promotions.
How this is calculated
Definitions: price = current selling price per unit, cost = unit cost, d = discount as a decimal.
- Discounted price = price × (1 − d)
- Original unit margin = price − cost; margin % = (price − cost) / price
- New unit margin = price × (1 − d) − cost; new margin % = new margin / discounted price
- Margin erosion ($) = original margin − new margin; erosion (percentage points) = original margin % − new margin %
- Break-even volume multiplier = (price − cost) / (price × (1 − d) − cost). Required volume increase = multiplier − 1
Assumptions: unit cost is constant regardless of volume; fixed costs are unchanged by the promotion; demand responds to the discount. These are estimates for planning, not accounting advice.
Worked example
Price $100, cost $60, discount 10%: sale price = $100 × 0.90 = $90.00. Original margin = $100 − $60 = $40.00 (40.0%). New margin = $90 − $60 = $30.00 (33.3%). Margin erosion = $10.00 (6.7 percentage points). Break-even multiplier = 40 / 30 = 1.333×, so sales volume must rise 33.3% to hold total profit flat.
Reference data
| Measure | Definition |
|---|---|
| Unit margin ($) | Selling price − unit cost |
| Margin % | (Selling price − unit cost) ÷ selling price |
| Markup % | (Selling price − unit cost) ÷ unit cost |
| Margin erosion | Original margin − discounted margin (in $ or percentage points) |
Source: standard accounting definitions (derived — no external table used on this page).
Method & sources
The break-even volume formula follows from holding total profit constant: original margin × original volume = new margin × new volume, so new volume ÷ original volume = original margin ÷ new margin. All figures are exact arithmetic on your inputs; the "rule of thumb" in the FAQ is labeled as a guideline, not a precise rule.
Frequently asked questions
Why does a 10% discount need more than 10% extra sales to break even?
Because a discount comes entirely out of your margin, not off the top. At $100 price and $60 cost, a 10% discount wipes out $10 of a $40 margin — a 25% cut in per-unit profit — so you must sell 33.3% more units just to hold total profit flat. The lower your starting margin, the bigger the sales lift required.
What is the 50%-margin rule of thumb for discounts?
The rule of thumb is that businesses with margins near 50% can tolerate modest discounts (around 10%) with only a moderate sales lift, while businesses with thin margins below 20% should avoid percentage discounts entirely — the required volume increase becomes extreme. For example, at 40% margin a 10% discount needs 33% more sales, but at 15% margin the same discount needs 200% more sales. Treat this as a rough guideline, not a formula.
How is this different from the discount deal comparator?
The discount deal comparator compares two deals side by side to find the cheaper final price — it is a shopper's tool. The discount impact calculator is a seller's tool: it shows how a discount erodes your margin and how much extra volume you need to make up for it.
When does a discount break even on its own?
A discount breaks even when actual sales growth meets or beats the required volume lift shown in the results. If the calculator says you need 33.3% more units and the promotion only delivers 20%, total profit falls. Track the actual lift after the promotion and compare it to the break-even figure.