Discount Profitability Calculator
What a sale price does to your margin — and how many extra sales you need to break even on it.
About this calculator
A discount comes straight out of profit, not revenue — cutting a £40 price by 20% might halve your profit per sale, meaning the promotion must double volume just to stand still. This calculator shows the margin before and after, and the volume uplift a promotion must achieve to break even on it.
The formula
Worked example
Price £40, cost £24, discount 20%: profit falls £16 → £8; you need +100% more sales for the same total profit.
Common mistakes
- Judging a sale by revenue while profit quietly halves.
- Discounting products whose buyers would have paid full price anyway.
- Stacking a discount on top of paid-ad traffic that already carries a CAC.
Frequently asked questions
Assumptions & limitations
Constant unit cost; ignores second-order effects like basket-size changes during promotions.
Sources & verification
This calculator applies the standard formula published above to the figures you enter — it relies on no external statutory data. The formula and the worked example were checked by hand against each other.
Spotted an error or an out-of-date figure? Report it — corrections are prioritised over all other work (see our corrections policy).