Discount Calculator
Sale price, savings, and stacked discounts done correctly — they don't just add up.
Why stacked discounts don't just add up
A common assumption is that "20% off, then an extra 10% off" means 30% total savings — it doesn't. Each discount applies to the already-reduced price, not the original, so a 20% discount followed by 10% gives roughly 28% combined savings, not 30%: £100 becomes £80 after the first discount, then £72 after the second, not £70. This calculator applies discounts sequentially the way real stacked promotions actually work, and shows the true combined percentage alongside the final price.
Frequently asked questions
Do stacked discounts add together?
No — a 20% discount followed by a 10% discount gives 28% total savings, not 30%. Each discount applies to the already-reduced price, so stacked percentages always add up to slightly less than their simple sum.
How do I calculate the original price from a sale price?
Divide the sale price by (1 minus the discount as a decimal). A £70 sale price after 30% off means the original price was 70 ÷ 0.7 = £100.
Should tax be calculated before or after a discount?
In most checkout situations, tax is calculated after the discount is applied — the discount reduces the taxable amount first.
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