Stacked discounts
"30% off + an extra 10% at checkout": what do you actually pay? Calculate the final price when discounts are applied one after another, and the true total discount.
Why doesn't 30% + 10% equal 40% off?
Because the second discount is applied to the already discounted price, not the original one. On $100, 30% off brings you to $70; the extra 10% takes off $7 (10% of 70, not of 100), landing you at $63. The true discount is therefore 37%, not 40%. The general formula: final price = price × (1 − d₁) × (1 − d₂) × … The more discounts you stack, the wider the gap from the naive sum: 50% + 50% doesn't mean free merchandise, it's a 75% total discount.
How to use it during sales and promos
Stacked discounts are everywhere: clearance racks with "an extra 20% off at the register," coupons applied to your cart, promo codes on prices already slashed for Black Friday. Before deciding whether a deal is really worth it, work out the true discount and compare it with the price the same product sells for elsewhere: a "40% + 10%" (actually 46%) only beats a flat "50% off" if the starting price is the same. This tool provides estimates for your shopping only and is not financial advice, for major financial decisions, consult a professional.