Price and discount
Leave the second discount at 0 if there's only one.
Last updated 3 September 2026
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.
Stacked discounts do not add up
This is the single most useful thing to know about discounts. Taking 20% off and then a further 30% off is not 50% off. The second discount applies to the already-reduced price, so a $200 item becomes $160, then $112 — a total reduction of 44%, not 50%. Six percentage points, or $12, sits between the intuition and the arithmetic.
The gap widens as the discounts get larger. Stacking 50% and 50% leaves you at 75% off, not free. Stacking three 30% discounts gives 65.7% off rather than 90%. Whenever a retailer advertises "extra 20% off sale prices", the honest headline number is always lower than the two figures added together.
Working backwards from a sale price
The reverse question comes up just as often: something is marked at $63 after 30% off, so what did it cost before? The answer is $63 ÷ 0.70 = $90. The common mistake is adding 30% back to $63, which gives $81.90 and is wrong by $8.10, because the 30% was taken off the larger original figure, not the smaller sale one.
The same asymmetry explains a fact that surprises people: a 50% fall needs a 100% rise to recover. A $100 item cut to $50 has lost half its value, but getting from $50 back to $100 is a doubling. Percentage decreases and increases are never symmetrical, which matters as much for investments and traffic figures as it does for shopping.
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.
Is 20% off then 30% off the same as 50% off?
No. The second discount applies to the already-reduced price. A 200 item becomes 160, then 112 — a total of 44% off rather than 50%. Stacked discounts always come out lower than the two percentages added together.
How do I find the original price from a sale price?
Divide, do not add back. If 63 is the price after 30% off, the original is 63 ÷ 0.70 = 90. Adding 30% to 63 gives 81.90, which is wrong because the discount was calculated on the larger original figure.
Why does a 50% loss need a 100% gain to break even?
Because each percentage is measured against a different base. Falling from 100 to 50 removes half of 100. Climbing from 50 back to 100 adds a whole 50 to a base of 50, which is a 100% increase. Percentage rises and falls are never symmetrical.