How to work out a discount
Multiply the price by the discount as a decimal to find the saving, then subtract it. Or, quicker, multiply by (1 − discount). £50 with 20% off = £50 × 0.8 = £40, a saving of £10.
Stacked discounts are not added together
Shops often advertise "20% off, plus an extra 10% at the till". The second discount comes off the already-reduced price, so it is worth less than it sounds. £50 × 0.8 = £40, then £40 × 0.9 = £36. That is a real total discount of 28%, not 30%. The order doesn't matter (10% then 20% gives the same £36), but adding the percentages always overstates the saving.
Finding the original price
If you know the sale price and the percent off, divide by (1 − discount). An item at £68 after 15% off was £68 ÷ 0.85 = £80. The percentage calculator can do the reverse sums.
Is it really a bargain?
UK consumer law (the Consumer Protection from Unfair Trading Regulations and the Digital Markets, Competition and Consumers Act 2024) means "was" prices shouldn't be misleading. A reference price should be one the product was genuinely sold at for a fair period. Price-tracking sites can show whether a "was £100" item usually sells for less. Remember that UK shelf prices already include VAT. If you are a business comparing ex-VAT prices, use the VAT calculator.
Worked example
A £129.99 coat at 30% off is £90.99, saving £39.00. With an extra 15% student discount it is £77.34, a real total discount of 40.5%.
Frequently asked questions
How do I calculate 20% off?
Multiply the price by 0.8. £60 with 20% off is £48.
Is 20% off plus 10% off the same as 30% off?
No. It is 28% off, because the 10% is taken from the already-reduced price.
How do I find the original price before a discount?
Divide the sale price by (1 − discount). £40 after 20% off was £40 ÷ 0.8 = £50.
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