How to Calculate a Discount
Calculating the sale price after a discount requires two simple steps. First, convert the discount percentage to a decimal (divide by 100). Then multiply the original price by (1 − discount decimal).
For a $80 item at 30% off: discount decimal = 0.30. Sale price = $80 × (1 − 0.30) = $80 × 0.70 = $56. Amount saved = $80 − $56 = $24.
Mental math shortcut for common discounts: 10% off = divide by 10. 25% off = divide by 4. 50% off = divide by 2. 20% off = divide by 5. For 30% off, take 10% (divide by 10) and multiply by 3, then subtract from original.
Retailers use percentage discounts strategically. A '40% off plus an additional 20% off' is NOT the same as 60% off. The compounded discount is: 40% off = pay 60%, then 20% off that 60% = pay 48% of original. Total discount is 52%, not 60%.
Stacked Discounts and Coupon Strategy
Understanding how stacked discounts work can save significant money. When multiple discounts apply, they multiply rather than add. A 20% site-wide sale plus a 15% coupon code gives: Pay 80% × 85% = 68% of original, or a combined 32% discount — not 35%.
This also explains why the order of discount application doesn't matter mathematically. Whether you apply 20% off first or 15% off first, 80% × 85% = 85% × 80% = 68% of original price.
Cashback stacking: If your credit card offers 3% cashback at a retailer and the retailer has a 20% sale, your effective total discount is 20% + 3% of 80% = 20% + 2.4% = 22.4%. Serious bargain hunters calculate this to find when the actual cost of an item hits their target price.