Discount stack calculator

Stacked discounts multiply. Thirty per cent off then twenty per cent off leaves 56% of the original price — an effective 44% discount, not 50%. The shortfall grows as the individual percentages grow.

The order does not matter — 30% then 20% gives the same answer as 20% then 30% — but the intuition that they add certainly does. The mathematical reason is that the second discount applies to the already-reduced price, so it takes a percentage of a smaller number. Two 50% discounts leave a quarter of the price, not nothing. This matters most on the retailer side, where a stack of promotions each individually approved can quietly take a product below cost.