Price and discount
Leave the second discount at 0 if there's only one.
Why stacked discounts don't just add up
"20% off, then an extra 10% off" sounds like 30% off, but it isn't. The second discount applies to the already-reduced price, not the original one, so the true saving is always a little less than the sum of the two percentages suggests.
On a £100 item: 20% off brings it to £80. A further 10% off £80 is £8, bringing the final price to £72 — a 28% saving overall, not 30%. The gap grows as the discounts get bigger, which is exactly why stores like advertising two smaller discounts stacked rather than one combined number.
Common questions
Do two discounts of 20% and 10% add up to 30% off?
No. The second discount applies to the already-reduced price, not the original, so it comes to 28% off, not 30%. £100 at 20% off is £80; a further 10% off £80 is £72, which is 28% below the original £100.
How do I calculate a discount by hand?
Multiply the price by the discount percentage, divide by 100, and subtract that from the price. For 20% off £50: 50 × 20 ÷ 100 = 10, so the final price is £40.
Is my data saved anywhere?
No. Everything is calculated in your browser and nothing is sent anywhere or stored.