Discount calculator
Find the sale price and how much you save, from either a percentage off or a fixed amount off. It is quick enough to use while you are standing in a shop.
Uses a standard published formula, explained below. Everything is calculated in your browser, and nothing you enter is sent to a server. This is not financial advice.
The price
You pay
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Original price
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You save
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Effective discount
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Show the working
—Stacked discounts do not add up
This is the most useful thing to know when you shop. An extra 20% off an item that is already 30% off is not 50% off in total. It is 44% off.
The second discount is taken from the reduced price, not from the original one. Starting at 100, a 30% discount brings the price down to 70. Taking another 20% off 70 brings it to 56. You pay 56, which is 44% less than the original price, not 50%.
The gap grows as the discounts get bigger, and it always works in the shop's favor. A sign offering "30% off plus an extra 20%" is accurate, but most people read it as a bigger saving than it really is.
Finding the original price from a sale price
To find what an item cost before the discount, divide instead of subtracting. If an item costs 75 after 25% off, its original price was 75 divided by 0.75, which is 100. Adding 25% to 75 would give 93.75, which is wrong.
This is the same trap that catches people when they remove sales tax from a price, and it is just as common.
Percentage off or a fixed amount off
Which one saves you more depends on the price, and it is worth knowing when a shop gives you the choice.
A fixed 20 off saves more than 20% off whenever the item costs less than 100. Above 100, the percentage saves more, and the difference keeps growing. On an item costing 500, 20% off saves 100, while the fixed discount still saves only 20.
Shops know this, which is why fixed-amount vouchers usually come with a minimum spend. The voucher is there to make you spend more, not to save you money.
Checking whether a sale is a real saving
Before you count a discount as a saving, check two things. First, check whether the original price was ever genuinely charged. Many countries have rules requiring an item to have been sold at the higher price for a period before it can be advertised as reduced, because inflated "was" prices used to be common. Second, ask yourself whether you actually wanted the item. A 70% discount on something you will never use is not a 70% saving; it is money spent on nothing.
Frequently asked questions
How do I calculate a discount?
Multiply the price by the discount percentage and divide by 100 to find the saving, then subtract the saving from the price. Or multiply the price by one minus the discount as a decimal to get the sale price directly.
What does 20% off mean?
It means you pay 80% of the original price. On an item costing 50, you pay 40 and save 10.
Do stacked discounts add together?
No. Thirty percent off followed by twenty percent off is 44% off in total, not 50%, because the second discount is taken from the already reduced price.
How do I find the original price from a sale price?
Divide the sale price by one minus the discount as a decimal. An item costing 75 after 25% off originally cost 75 ÷ 0.75, which is 100.
Is a percentage or a fixed amount off better?
A fixed amount saves more on cheaper items, and a percentage saves more on expensive ones. A fixed 20 off beats 20% off on anything under 100, and loses on anything over 100.
Can I trust the original price shown on a sale tag?
Not always, so it is worth checking. Many consumer protection laws require the higher price to have been charged for a real period beforehand, because inflated original prices used to be common.