Discount Calculator
The sale price, the percentage off, or the original price worked backwards — plus the one shops rely on you getting wrong: two discounts in a row do not add up.
Runs on your device — nothing is sent anywhere“An extra 20% off sale items”. This comes off the already-reduced price, which is why it saves less than it sounds.
What it costs now. The discount is measured against the original price above.
No currency symbol, because the arithmetic is the same everywhere. Tax, where it is added at the till, comes after the discount and is not included here.
How it works
No account, and the numbers never leave your device.
Pick the question
The sale price, the percentage off two prices represent, or the original price worked backwards from what you paid.
Type the numbers
The answer updates as you type. There is no currency symbol because the sum is the same in all of them.
Add a second discount if there is one
"An extra 20% off sale prices" is a different sum from 20% off, and the calculator shows what the two together actually come to.
What people are working out
Whether a sale is worth it
"40% off" on a price that went up last month is a different thing from 40% off, and the only defence is knowing the real numbers.
Two discounts at once
A sale price plus a voucher code. They multiply rather than add, and the difference is usually several per cent.
Working back to the original price
You know what you paid and the discount, and want the list price — for an expense claim, a return, or an insurance form.
Checking what a shop is claiming
A "50% off" label on a price that is 60% of the original is a straightforward error, and it happens.
Why two discounts never add up
Thirty per cent off, then an extra twenty per cent off, is not fifty per cent off. It is forty-four.
This is the single most useful thing on this page, because it is not a trick of arithmetic — it is how every stacked promotion in every shop works, and the gap between what it sounds like and what it is runs to real money.
The sum
Take a price of 100.
Thirty per cent off leaves 70. The extra twenty per cent comes off that, not off the original — twenty per cent of 70 is 14, so you pay 56.
You saved 44 from 100. Forty-four per cent, not fifty.
The shortcut is to multiply what is left: 0.70 × 0.80 = 0.56, so you pay 56% and save 44%. Chaining any number of discounts works the same way, and the more you chain the wider the gap grows.
| Advertised | Sounds like | Actually | You pay |
|---|---|---|---|
| 20% then 10% | 30% off | 28% off | 72.00 |
| 30% then 20% | 50% off | 44% off | 56.00 |
| 50% then 20% | 70% off | 60% off | 40.00 |
| 50% then 50% | 100% off | 75% off | 25.00 |
| 70% then 30% | 100% off | 79% off | 21.00 |
The last two rows are the point. Stacked discounts can never reach 100% — halving something repeatedly gets closer to zero and never arrives.
Working backwards is division, not addition
You paid 84 after 30% off. What was the original price?
The wrong answer, and the common one, is to add 30% back: 84 + 25.20 = 109.20. That is not it.
Paying after a 30% discount means paying 70% of the original, so the original is 84 ÷ 0.70 = 120. The right operation is dividing by what is left, not multiplying by what came off.
The two answers differ by nearly eleven, and the gap grows with the discount. At 50% off, adding back gives you three-quarters of the true original.
Discount and tax, in that order
Where tax is added at the till, it goes on the discounted price. A 100 item at 20% off with 8% tax is 80 × 1.08 = 86.40, not 100 × 1.08 × 0.80 — which happens to be the same number, because multiplication does not care about order.
So the order genuinely does not matter for the total. It matters for the receipt, and for arguing about it.
The percentage a shop is quoting
Discounts are measured against the original price, always. A jacket down from 120 to 84 is 36 off, and 36 ÷ 120 = 30%. Dividing by the sale price instead gives 43%, which is the answer to a different question — "how much more is the original than the sale price" — and is how an honest mistake becomes a misleading claim.
What the number cannot tell you
Whether the original price was ever charged. A discount is a percentage of whatever the shop says the item used to cost, and in many places that claim is only loosely regulated. Several jurisdictions require the reference price to be the lowest charged in the previous thirty days, precisely because of this.
The arithmetic here is exact. What it is arithmetic about is somebody else's number.
Common questions
How do I calculate a discount?
Multiply the price by the discount and subtract, or more directly multiply by what is left: 30% off is × 0.70. A price of 120 at 30% off is 120 × 0.70 = 84.
Is 30% off then 20% off the same as 50% off?
No. The second discount comes off the already-reduced price, so the pair is 44% off, not 50%. Multiply what is left: 0.70 × 0.80 = 0.56, meaning you pay 56% of the original.
How do I find the original price from what I paid?
Divide by what is left, not add the percentage back. Paying 84 after 30% off means 84 is 70% of the original, so the original is 84 ÷ 0.70 = 120. Adding 30% back would give 109.20, which is wrong.
How do I work out what percentage off something is?
Subtract the sale price from the original, divide by the original, and multiply by 100. From 120 to 84 is 36 ÷ 120 = 30%. Dividing by the sale price instead is the usual error.
Can stacked discounts ever reach 100% off?
No. Each discount takes a fraction of what remains, so the price gets closer to zero without arriving. 50% then 50% is 75% off, not 100%.
Does tax go on before or after the discount?
After, where tax is added at the till — the tax is charged on what you actually pay. The total works out the same either way, since multiplying in a different order gives the same result.
Why is there no currency symbol?
Because the sum is identical in every currency. The numbers come back in whatever units you typed them in.
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Every one of them runs on your device. No uploads, no accounts.