What this calculator does
This calculator shows the sale price a discount produces and, more importantly, what it does to the profit behind that sale. It reports the margin that survives the promotion and how many extra units you would need to sell just to end up with the same profit you had before the discount started.
How to use it
- Enter the regular price the product normally sells at.
- Enter the product cost and shipping cost so the calculator knows your landed cost.
- Enter the discount percentage you are considering.
- Read the sale price and the margin that remains after the discount.
- Check the extra units figure — that is the volume increase the promotion has to deliver just to break even against not running it.
The formula, explained
The last line is the one worth sitting with. A discount reduces profit per unit, so the promotion only makes sense if it increases volume by more than the profit it gives away. On thin margins that required increase can be enormous.
There is a second cost that no formula captures: discounts train customers to wait. A store that runs a sale every month teaches its audience that the regular price is optional, which is a slow and expensive habit to unwind.
A worked example
A product sells for 49.99 with a landed cost of 23.00, giving a profit of 26.99. You are considering 20% off.
The sale price becomes 39.99, and profit falls to 16.99 — a 37% cut in profit for a 20% cut in price. To make the same total profit you would need to sell about 59% more units. If the promotion cannot plausibly do that, it is costing you money even while the order count rises, which is exactly how a busy sale week can end with a worse month.
| Regular price | 49.99 |
|---|---|
| Discount | 20% |
| Sale price | 39.99 |
| Profit before | 26.99 |
| Profit after | 16.99 |
| Extra units to match | +58.9% |
What a good result looks like
How much discount a product can absorb depends entirely on the margin underneath it.
| Range | What it means |
|---|---|
| Margin above 50% | Can carry a 20% to 30% discount and stay comfortably profitable. |
| Margin 35% to 50% | 10% to 20% is sensible. Beyond that the profit drops sharply. |
| Margin 20% to 35% | Keep discounts under 10%, or use free shipping instead. |
| Margin under 20% | Discounting sells at or below cost. Add value rather than cutting price. |
Common mistakes
- Discounting to fix a conversion problem. If the page is not converting, the price is rarely the only reason. Discounting hides the real issue and costs margin permanently.
- Stacking codes with existing sale prices. Sitewide codes applied on top of already-reduced items can quietly take orders below cost. Exclude sale items from code eligibility.
- Forgetting that fees stay the same. Payment fees are charged on the discounted price, but shipping and product costs do not fall at all. The margin squeeze is entirely on your side.
- Running permanent sales. A discount that never ends is just a price. Worse, it removes the tool you would otherwise use to create genuine urgency.
- Measuring promotions by revenue. Sale weeks almost always show higher revenue. Only profit tells you whether the promotion was worth running.
Frequently asked questions
How do I calculate a sale price?
Multiply the regular price by one minus the discount as a decimal. Twenty percent off 49.99 is 49.99 × 0.8, which is 39.99. The calculator does this and then shows you the part that matters — what happens to profit at that new price.
What discount can I afford to offer?
It depends on your margin. As a rough guide, a discount of roughly a third of your margin percentage is usually safe: on a 45% margin, a 15% discount still leaves a workable profit. Anything approaching your margin percentage sells at close to cost.
Is free shipping better than a percentage discount?
Often, yes. Free shipping has a high perceived value and a fixed, known cost to you, while a percentage discount scales with the order value and can cost far more on larger baskets. It also avoids anchoring customers to a lower price.
How do I run a sale without damaging my brand?
Give it a reason and an end date. Seasonal events, product launches and clearance of specific items all justify a temporary price. Open-ended sitewide discounts with no explanation are the ones that erode price expectations.
Should I show the crossed-out original price?
Only if it is genuinely the price you normally charge. Many jurisdictions regulate reference pricing, and beyond the legal question, customers are good at spotting an inflated original. A real saving shown honestly converts better than an invented one.
How this fits with your other numbers
Discounting is the most expensive marketing channel most stores use, because the cost comes entirely out of margin rather than being shared with anyone. Before running a promotion, look at the extra units figure this calculator produces and ask honestly whether the campaign can deliver that much additional volume.
There are usually cheaper alternatives that feel similar to the customer: free shipping, a gift with purchase, a bundle, or an extended guarantee. Each has a known fixed cost rather than a percentage that scales with order value, and none of them teach your audience to wait for the next sale — which is the real long-term price of a discount habit.