The 20% sale that costs you 35%

Here is the arithmetic nobody does in the stationery aisle. You sell something at ten pounds that costs you five. Margin: five pounds. You run 20 percent off — new price eight pounds, new margin three. You just gave away 40 percent of your profit on every unit, not 20. To make the same money as before, you need to sell 67 percent more units.

Ask yourself honestly: has a sale ever lifted your volume 67 percent?

Sometimes yes — and then discounts are a weapon. Often no — and then the busy weekend of the sale is actually your quietest week of the quarter in profit terms, disguised by a full shop.

The three questions before any discount

First: what is the real margin give-up, in pounds, per unit? Not the ticket percentage — the profit percentage. Second: what volume lift do I need to break even, and is that lift plausible for this product? Elastic products (treats, fashion, gifts) can double on a good promotion. Inelastic ones (necessities people buy anyway) mostly reprice existing demand — you fund a discount for people who were buying regardless. Third: what happens after? A discount that merely pulls next month’s purchases forward is a loan, not a sale.

Simulate it first

The Discount Builder in Pulse runs this arithmetic on your actual numbers before you commit: your real margin, your product’s real velocity, the honest break-even lift, and a verdict — profit-making, break-even, or margin-burning. Its sibling for restaurants does the same for menu prices. Thirty seconds of simulation against your own till data beats an hour of hopeful guessing.

Discounts are a tool, not a reflex

The point is not never discount. Clearing dead stock, rewarding loyalty, driving a genuinely quiet daypart — all legitimate. The point is that a discount is a purchase: you are buying volume, and paying in margin. Know the price of what you are buying before you buy it. Your till already knows. Now the simulator does too.