Discount Calculator
Find the final price after a discount and how much you save. The stacked mode handles "extra 10% off sale prices", where the second cut applies to the reduced figure.
Your data never leaves your browser. This tool runs entirely on your device.
Final price
80
- You save
- 20
- Original price
- 100
100 − (100 × 20 ÷ 100) = 80
The formula
A discount is a percentage decrease. Multiply the price by the percentage to find the saving, then subtract it — or multiply directly by what remains.
Multiplying by (1 − rate) is the quicker route: a 30% discount means paying 70% of the price, so £80 × 0.70 = £56 in one step.
Final price = Price × (1 − Discount ÷ 100)
Stacked discounts do not add up
A shop offering "20% off, plus an extra 10% off sale items" is not giving you 30% off. The second discount applies to the already-reduced price, not the original.
On £100: the first cut leaves £80, and 10% off that is £8, giving £72. That is 28% off in total, not 30%. The gap widens as the discounts get larger — 50% plus 50% is 75% off, not free.
100 → −20% → 80 → −10% → 72 (28% off, not 30%)
Working backwards from the sale price
To check an advertised discount, divide the sale price by the original and subtract from 1. If a £120 item is on sale for £90, then 90 ÷ 120 = 0.75, so the discount is 25%.
This is worth doing when a "was" price looks inflated — the percentage claimed and the percentage delivered are not always the same.
Frequently asked questions
How do I calculate 20% off a price?
Multiply the price by 0.80, which is what remains after taking 20% away. For £80: 80 × 0.80 = £64, saving £16.
Is 20% off plus 10% off the same as 30% off?
No. The second discount applies to the already-reduced price, so the combined effect is 28% off, not 30%. Stacked discounts always come to less than their sum.
How do I work out the discount percentage from two prices?
Divide the sale price by the original price and subtract the result from 1, then multiply by 100. From £120 to £90: 1 − (90 ÷ 120) = 0.25, so 25% off.
Should VAT be applied before or after the discount?
After. The discount reduces the taxable amount, so VAT is charged on the discounted price. Applying VAT first and then discounting the gross gives the same final figure, but the VAT line would be wrong on the invoice.
Related tools
- Percentage Decrease CalculatorFind the percentage decrease between two values, or reduce a starting figure by a percentage. The working is shown so you can check the result.
- VAT CalculatorAdd VAT to a net price, or work backwards from a gross price to find the tax it contains. Both directions show the net, VAT and gross amounts.
- Percentage CalculatorAnswer the three questions people actually ask about percentages: what is X% of Y, X is what percent of Y, and how much did a value change. Each answer shows its working.
- Percentage Increase CalculatorFind the percentage increase between two values, or apply an increase to a starting figure. The working is shown so you can check the result.