🏷️ Discount Calculator

Discount Calculator - Sale Price, Percentage Off & Stacked Discounts

Discount math looks simple until a store advertises "an extra 10% off already-reduced prices," or you need to figure out what an item cost before a sale. This calculator handles the four most common discount questions: finding a sale price, finding what percentage off two prices represent, working backward to the original price, and correctly combining multiple stacked discounts.

Why Stacked Discounts Aren't What They Seem

Retailers often advertise "20% off, plus an extra 10% off" in a way that makes shoppers assume a 30% total discount. In reality, discounts stack multiplicatively: each discount applies to the already-reduced price, not the original. A $100 item with 20% off becomes $80, and a further 10% off that $80 gives $72 - a combined discount of 28%, not 30%. The gap grows larger with bigger discounts or more stacked layers, so it's always worth calculating the real final price rather than adding percentages in your head.

Working Backward: Finding the Original Price

A common mistake when reversing a discount is adding the percentage back to the sale price instead of dividing. If an item is $60 after a 25% discount, adding 25% of $60 back gives $75 - the wrong answer. The correct approach divides the sale price by (1 - discount as a decimal): $60 ÷ 0.75 = $80, the true original price. This distinction matters when comparing a "sale price" against a claimed "original price" to judge whether a discount is genuine.