How to calculate discounts and sale prices

Multiply the original price by the discount percentage to find the saving, then subtract it. A 25% discount on 80 saves 20, leaving a sale price of 60.

There is a shortcut: multiply the price by 1 minus the discount as a decimal. 80 × 0.75 = 60 gives the sale price in one step.

Two discounts do not simply add up. A 20% discount followed by a further 10% off the reduced price is 0.80 × 0.90 = 0.72 of the original, which is 28% off in total, not 30%.

The order does not change the final price, but each discount always applies to the price left after the previous one.

If you know the sale price and the discount, divide the sale price by 1 minus the discount. A sale price of 60 after 25% off means the original price was 60 ÷ 0.75 = 80.

A common mistake is to add 25% back onto 60, which gives 75. That is wrong because the discount was taken from the original price, not from the sale price.

Compare the final price with what other sellers charge, not just with the crossed-out price. A large discount from an inflated price may still be no bargain.

Remember tax and shipping. Apply sales tax or VAT to the discounted price, and include delivery costs when comparing offers.