Discount calculator with stacked discounts and margin
Enter the list price and a discount to get the sale price and the amount saved. Add a second discount to see what stacking really does, and enter your cost to check how much margin is left after the promotion.
Calculator
Applied to the already reduced price.
Shows the margin left after the discount.
Result
- Sale price
- Customer saves
- Total discount
- Margin after discount
The calculation runs in your browser; the numbers you enter are not sent anywhere.
Sale price = list price × (1 − discount). Two discounts multiply rather than add: 10% then 5% is a 14.5% discount, not 15%. A 10% discount on an item with a 30% margin leaves a margin of only about 22%.
How the calculator works out a discount
A percentage discount is taken from the list price; a fixed discount is simply subtracted from it. If you add a second discount, it is applied to the price that is left after the first one, which is how “extra 5% off sale prices” works in practice.
These are the formulas used:
- Sale price = list price × (1 − discount %) or list price − discount amount
- With a second discount: sale price × (1 − second discount %)
- Total discount = (list price − final price) ÷ list price
Stacked discounts do not add up
Because the second percentage applies to a smaller number, two discounts in a row always give less than their sum. The difference is small at low rates and grows quickly at higher ones.
Compare what the discounts seem to promise with what the customer actually gets:
| First | Second | Looks like | Actual |
|---|---|---|---|
| 10% | 5% | 15% | 14.5% |
| 20% | 10% | 30% | 28% |
| 30% | 20% | 50% | 44% |
What a discount does to your margin
The discount comes straight out of your profit, not out of your cost. On an item that costs 70 and sells for 100, a 10% discount cuts the profit per unit from 30 to 20. The margin drops from 30% to about 22%, and you need to sell 50% more units just to earn the same gross profit.
That is why it pays to enter the cost before you agree to a discount. A promotion can still be worth running for slow-moving stock or to win a regular customer, but you should decide that knowing the real number.
Practical scenario
Example: 25% off a pair of shoes
A shoe shop sells a pair for 80 that costs 45. At full price it earns 35 per pair, a 43.75% margin. With 25% off, the price is 60 and the profit falls to 15, a 25% margin. To earn the same 35 the shop now needs to sell about 2.3 pairs instead of one.
Step-by-Step Implementation
1. Enter the list price and discount
Choose whether the discount is a percentage or a fixed amount and type it in. Add a second discount only if you really stack them.
2. Add your cost
Enter the unit cost to see the margin left at the sale price. Picking a currency is optional.
3. Apply it in GiroPS
On GiroPS quotes, orders and invoices you can give each line a percentage or fixed discount and add a discount to the whole document. Tax is calculated after the discounts, so totals stay consistent.
Common Pitfalls & How to Avoid Them
Frequently Asked Questions
How do I calculate a percentage discount?
Multiply the price by (1 − discount). An item priced 120 with 15% off costs 120 × 0.85 = 102, so the customer saves 18.
How do I find the discount percentage between two prices?
Divide the difference by the original price. A price cut from 80 to 68 is (80 − 68) ÷ 80 = 15% off.
Is 10% plus 10% the same as 20%?
No. The second 10% is taken from 90, so the final price is 81 and the total discount is 19%.
Should the discount come before or after tax?
A percentage discount gives the same rate on prices with or without tax; a fixed amount does not. Most invoices take the discount from the net amount and calculate tax afterwards, which is how GiroPS works.