Discount and stacked-discount calculator
Find the sale price and the amount saved for any percentage discount.
This works out a sale price, the amount saved, and the effect of stacked discounts, in your browser. The arithmetic that catches people out is stacking: 20 percent off followed by another 10 percent off is not 30 percent off. The second discount applies to the already-reduced price, so the combined effect is 28 percent — a difference retailers rely on and shoppers routinely miscalculate. Stacked discounts multiply their remainders: 0.8 × 0.9 = 0.72, leaving 72 percent of the original and a 28 percent saving. On a $200 jacket that is $144, not the $140 a naive addition suggests. The order the discounts are applied never changes the result, because multiplication commutes. A fixed-amount coupon behaves differently and is worth more when applied after a percentage cut than before it, which is why terms usually specify the sequence.
About the Discount Calculator
See exactly what you'll pay — and exactly how much you save — for any percentage-off discount. Enter the original price and the discount percent to instantly get the sale price and your savings.
How to use the Discount Calculator
- 01Enter the item's original price.
- 02Enter the discount percentage being offered.
- 03Read the final sale price and your savings instantly.
Why use our Discount Calculator
- 01
Sale price + savings
Both numbers shown side-by-side so you know the real deal.
- 02
Any percent
Works for any discount from 0% to 100%.
- 03
Instant results
Numbers update as you type — perfect for shopping in store.
- 04
Private
Calculations run locally — nothing is sent anywhere.
Do stacked discounts add together?
Each successive discount applies to whatever the price is at that point, not to the original. Take £100 with 20 percent off, giving £80; a further 10 percent off that £80 removes £8, not £10, leaving £72. The total reduction is 28 percent rather than 30. The general formula for combining two discounts is 1 − (1 − a)(1 − b), so 20 and 10 percent combine to 1 − 0.8 × 0.9 = 0.28. The order does not matter — applying 10 percent then 20 percent gives the same £72 — which is worth knowing when a retailer implies that a particular sequence is more advantageous. The effect compounds with more layers: three successive 20 percent discounts give 48.8 percent off rather than 60. Understanding this is the difference between evaluating a 'extra 10 percent off sale prices' offer correctly and overestimating it, which is precisely the response such offers are designed to produce.
Percentage off versus multi-buy offers
Retail promotions are frequently structured to be hard to compare, and converting everything to a unit price or an equivalent percentage is the only reliable method. Buy one get one free is 50 percent off when you want two items and no discount at all when you want one. Three for the price of two is 33.3 percent off, not 50. Buy one get one half price is 25 percent off across the pair. A £10 voucher on a £40 spend is 25 percent, but on a £60 spend it is 16.7 percent, so the value falls as the basket grows — the opposite of a percentage discount. Bundle pricing is the hardest to evaluate because it mixes items you wanted with items you did not, and the honest comparison is against the cost of buying only what you actually needed at its best available price. The general rule is that any offer requiring you to spend more to save more should be assessed on total outlay, not on the discount percentage.
Reference prices, tax and knowing what the saving really is
A discount is only meaningful relative to a genuine reference price. Consumer protection rules in the UK and EU require that a 'was' price must have been the actual selling price for a defined period, and the EU's Omnibus Directive since 2022 requires price-reduction announcements to reference the lowest price applied in the previous thirty days — rules that exist precisely because inflated reference prices were widespread. Recommended retail prices are set by manufacturers and are frequently well above what anything actually sells for, so a discount from RRP can be no discount at all. The practical check is to compare against what the item has recently sold for elsewhere rather than against the stated original. On tax, note that a discount is applied before sales tax or VAT is calculated, so the tax falls on the reduced price and your actual saving includes the tax you no longer pay — a 20 percent discount on a VAT-inclusive price saves 20 percent of the total, tax included.
What offers are actually worth
| Offer | Real discount | Condition |
|---|---|---|
| 20% then extra 10% | 28% | Not 30% — applies to reduced price |
| Buy one get one free | 50% | Only if you want two |
| 3 for the price of 2 | 33.3% | Only if you want three |
| Buy one get one half price | 25% | Across the pair |
| £10 off £40 spend | 25% | Falls to 16.7% on a £60 spend |
| Three successive 20% cuts | 48.8% | Not 60% |
Combine discounts with 1 − (1 − a)(1 − b). Order never changes the result.
Frequently asked questions
Is 20% off then 10% off the same as 30% off?
No. The second discount applies to the already-reduced price, so the combined effect is 28%. Use 1 − (1 − a)(1 − b) to combine them.
Does the order of stacked discounts matter?
No. Applying 10% then 20% gives exactly the same result as 20% then 10%, because multiplication is commutative.
How much is buy one get one free worth?
50% off if you genuinely want two items. If you only wanted one, it is no discount at all.
Is three for the price of two 50% off?
No, 33.3%. You pay for two and receive three, so the saving is one item across three.
How do I compare a voucher to a percentage?
Divide the voucher by the spend it requires. £10 off £40 is 25%, but the same voucher on £60 is only 16.7% — voucher value falls as the basket grows.
Can I trust the 'was' price?
Regulations require it to have been a genuine selling price, and the EU Omnibus Directive requires reference to the lowest price in the previous 30 days. Compare against recent prices elsewhere anyway.
Is a discount applied before or after tax?
Before. Tax is calculated on the reduced price, so your saving includes the tax you no longer pay on the discounted amount.
How do I evaluate a bundle?
Compare against the cost of buying only the items you actually wanted at their best available price, ignoring the ones the bundle added.
Is my data uploaded?
No. Everything is calculated in your browser.
Last updated
Price-reduction rules per EU Directive 2019/2161 (Omnibus), applicable from 2022, and UK Chartered Trading Standards Institute pricing practices guidance.