Discount calculator

Watch out for inflated discounts

Not every discount is real: sometimes the "original price" is quietly raised shortly before a sale so the markdown looks bigger than it is, a classic trick around Black Friday and Prime Day. The true discount should always be measured against the price the item actually sold for in the weeks before the promotion, not against a made-up list price.

How to tell whether a deal is genuine

The most reliable check is the price history: if today's price really is the lowest it has been in recent months, the deal is real. Price-tracking sites and browser extensions chart how an item's price has moved over time and flag verified all-time lows, so a ten-second look at the graph tells you whether that "50% off" banner deserves your money or your skepticism.

The sum, and how to do it in your head

Final price = price × (1 − discount ÷ 100). The quick way, in front of the shelf, is to think in terms of what's left rather than what's taken off: −30% means paying 70%, so you multiply by 0.7. On 89: 10% is 8.90, 30% is three times that (26.70), and the final price is 62.30.

Two discounts in a row don't add up

A −20% followed by a −10% isn't −30%, it's −28%, because the second applies to an already reduced price. With factors it's immediate: 0.80 × 0.90 = 0.72, that is 72% of the starting price. It also holds for a voucher applied on top of the sale price, and it holds in reverse order with the same result: the total discount doesn't change if you swap the two.

The same arithmetic explains something else useful: after a 20% discount, getting back to the old price needs a rise of 25%. It's why the price you see after the sales looks like it went up more than it had come down.

Nearby tools

If you have the two prices and want the percentage, the page is Discount percentage; to apply any increase or reduction Increase or reduce by a %. To compare two packs of different weight there is Price per kg, and for the price with or without tax VAT calculator.