To calculate a discount, multiply the price by the discount as a decimal to get the saving, then subtract it — 25% off 80 saves 20 and leaves 60.
To calculate a discount, multiply the original price by the discount as a decimal to find what you save, then subtract it from the price. A 25% discount on 80 saves you 20 and leaves 60 to pay. The arithmetic is easy. What actually costs shoppers money is everything wrapped around it: stacked offers that add up to less than they appear, “buy two get one free” deals whose real percentage is never printed, and inflated original prices that make a modest reduction look generous. This guide covers the maths and then the tactics, so you can work out in a few seconds whether a deal is worth taking. The CalcRange Discount Calculator does the sums if you would rather not.
The Two Formulas
Amount saved = original price x (discount % / 100)
Sale price = original price x (1 – discount % / 100)
The second formula skips a step. Rather than calculating the saving and subtracting it, you work out what fraction of the price you still pay. A 30% discount means paying 70%, so multiply by 0.70 and you are finished.
Both need the discount as a decimal: 25% becomes 0.25, 5% becomes 0.05. If percentage conversion is where you slip up, our guide on calculating percentages covers the underlying method in full.
Worked Examples
25% off an item priced 80
- Saving: 80 × 0.25 = 20
- Sale price: 80 × 0.75 = 60
15% off an item priced 80
- Saving: 80 × 0.15 = 12
- Sale price: 80 × 0.85 = 68
30% off an item priced 45
- Saving: 45 × 0.30 = 13.50
- Sale price: 45 × 0.70 = 31.50
Calculate a Discount
Enter the price and discount into the CalcRange Discount Calculator for the sale price and the amount saved. If you are shopping in another currency, the currency converter tells you what the deal is worth back home.
Why Stacked Discounts Disappoint
An extra 10% off an already 20% reduced item is not 30% off. It is 28%.
Start with 100. The first discount takes it to 80. The second applies to that reduced 80, not the original, so it removes 8 rather than 10, leaving 72. You paid 72 instead of the 70 that a straight 30% would have given.
Combined multiplier = (1 – first discount) x (1 – second discount)
0.80 × 0.90 = 0.72, so you pay 72% and the true discount is 28%
The gap widens with bigger numbers. A 50% reduction followed by a further 50% off leaves you paying 25%, a 75% total discount rather than the 100% that adding them would imply. This is worth internalising, because “extra 20% off sale items” signage is designed to be read additively.
One thing that does work in your favour: the order does not matter. Applying 20% then 10% gives exactly the same result as 10% then 20%, since multiplication is commutative. If a shop claims one order is better for you, the claim is wrong.
Working Backwards From the Sale Price
Two situations need the reverse calculation: recovering the original price, and checking whether an advertised discount is real.
Original price = sale price / (1 – discount % / 100)
You paid 68 after a 15% discount. Original = 68 ÷ 0.85 = 80.
The trap here is instinctive and expensive. Adding 15% back to 68 gives 78.20, not 80, because the 15% was calculated on the original 80 rather than on the 68 you paid. Percentages taken off and added back are never symmetrical.
To verify a claimed discount instead, divide the saving by the original price. An item marked down from 250 to 175 saved you 75, and 75 ÷ 250 = 0.30, confirming the advertised 30%. This takes seconds and occasionally reveals that the maths does not support the sign.
Decoding Deal Formats
Shops rarely express multi-buy offers as percentages, because the percentages are less impressive than the wording.
| Offer | You get | Actual discount |
|---|---|---|
| Buy one get one free | 2 for the price of 1 | 50% |
| 3 for 2 | 3 for the price of 2 | 33.3% |
| Buy 3 get 1 free | 4 for the price of 3 | 25% |
| Buy 2 get 1 half price | 3 for the price of 2.5 | 16.7% |
The method is always the same: work out what you pay, divide by what you would have paid, and subtract from one. Buy two get one half price on 10 items means paying 25 for 30 of goods, and 5 ÷ 30 = 16.7%.
Every one of these carries a condition that a straight percentage does not: you have to buy the extra units. A 50% discount you can take on one item beats a “buy one get one free” on something you only wanted one of, because the second unit is not a saving if you would not have bought it.
Two phrases deserve suspicion. “Up to 70% off” guarantees only that at least one item somewhere carries 70% off, with everything else potentially far lower. And a discount from a “recommended retail price” tells you nothing if nobody was ever charging that price.
Percentage Off or Amount Off?
Given a choice between “20% off” and “5 off”, which is better depends entirely on the price.
The two are equal where 20% of the price equals 5, which is at a price of 25. Below that, the fixed amount wins: on a 15 item, 20% saves 3 while the fixed voucher saves 5. Above 25, the percentage wins: on a 60 item, 20% saves 12 against the voucher’s 5.
Finding the crossover takes one division. Divide the fixed amount by the percentage as a decimal, so 5 ÷ 0.20 = 25. Below the crossover take the cash, above it take the percentage.
Doing It in Your Head
Almost every common discount can be built from 10%, which is just moving the decimal point one place left.
- 10% of 240 = 24
- 20% = double it, so 48
- 5% = half of it, so 12
- 15% = 24 + 12 = 36
- 30% = 24 × 3 = 72
- 25% = a quarter, so 60
- 75% = three quarters, so 180
For the price you actually pay, it is usually faster to work with what remains. At 30% off, you pay 70%, and 70% of 240 is 240 − 72 = 168.
Common Mistakes
- Adding stacked discounts together. Multiply the remaining fractions instead: 20% and 10% give 28%, not 30%.
- Adding the percentage back to recover an original price. Divide by the remaining fraction instead.
- Treating “up to X% off” as the discount on the item you want. It is a ceiling across the whole range.
- Comparing a percentage against a fixed amount without checking the crossover price.
- Counting a multi-buy as a saving on units you did not want. Value the ones you would have bought anyway.
- Forgetting that tax may be applied after the discount, which changes the final figure in places where prices are quoted before tax.
Frequently Asked Questions
How do I calculate 20% off a price?
Multiply the price by 0.80 to get what you pay, or by 0.20 to get what you save. On a 45 item that is 36 to pay and 9 saved. The mental route is finding 10% by moving the decimal, then doubling it.
Is 20% off then 10% off the same as 30% off?
No, it comes to 28%. The second discount applies to the already-reduced price rather than the original, so it removes less than you might expect. Multiply the remaining fractions to get the true figure: 0.80 × 0.90 = 0.72, meaning you pay 72%.
How do I find the original price from a sale price?
Divide the sale price by one minus the discount as a decimal. Paying 68 after 15% off means the original was 68 ÷ 0.85 = 80. Do not add the percentage back, since that gives 78.20 and is wrong.
What percentage discount is buy one get one free?
Fifty percent, since you get two items for the price of one. The equivalent for “3 for 2” is 33.3%, and for “buy 3 get 1 free” it is 25%. All of them require buying the extra units, so the saving is only real if you wanted them.
Does the order of two discounts matter?
No. Applying 20% then 10% gives an identical result to 10% then 20%, because you are multiplying the same two fractions. Any claim that one sequence saves you more is mistaken.
Is a bigger percentage always the better deal?
Not necessarily. Sixty percent off an item priced at 200 saves 120, while 30% off a comparable item priced at 90 saves 27, so compare the final prices of things you would actually buy rather than the headline percentages. Discounts from inflated reference prices can also make a poor deal look strong.
How do I compare deals on different pack sizes?
Convert both to a unit price by dividing the total cost by the quantity. A discounted large pack sometimes works out dearer per unit than a smaller one at full price, and unit pricing is the only reliable way to see it.
The Bottom Line
Multiply by the remaining fraction to get the sale price, divide by it to work backwards, and never add stacked discounts together. Convert multi-buy offers into percentages before comparing them with straight reductions, and remember that a saving on units you did not want is not a saving at all. Most of this can be done in your head from 10%, and the discount calculator covers the rest. The habit worth building is the reverse check: divide the saving by the original price and see whether the sign is telling the truth.
Prices and offers in this article are illustrative examples used to demonstrate the calculations. Last reviewed: August 2026. Evergreen content — recommended editorial review: every 12 months.
Related: How to calculate stacked discounts (don’t add them)