The three discount calculations
Every discount question is one of three. Write the discount as a decimal first: 30% is 0.3.
- The sale price: original × (1 − discount). For 80 with 30% off that is 80 × 0.7 = 56, and you save 24.
- The percent off: (original − sale price) ÷ original × 100. From 80 down to 60 is 20 ÷ 80 × 100 = 25% off.
- The original price: sale price ÷ (1 − discount). If 60 is the price after 25% off, the original was 60 ÷ 0.75 = 80.
The percentage is always taken from the original price, which is why the reverse sum divides instead of adding the percentage back. Adding 25% to 60 gives 75, and 25% off 75 is only 56.25.
Discounts that stack
When a second discount comes off the already reduced price, the two multiply instead of adding. 30% off and then 20% off is 0.7 × 0.8 = 0.56 of the original price, so the combined discount is 44%, not 50%. Two discounts of 50% are 75% off, not 100%.
The order does not change a percentage result, because multiplication gives the same answer either way. A fixed amount is different: 10 off before a percentage discount and 10 off after it give different totals, so check how a coupon is applied.
The calculator shows the combined discount whenever you add a second one. For a page built around sale prices and coupons, see the sale price calculator.
Tax and rounding
In many places tax is charged on the price after the discount, but rules for coupons and manufacturer discounts vary, so check how your tax works. With a rate entered, the calculator adds the tax to the sale price: 100 with 25% off is 75, and 8% tax on 75 is 6, so the total is 81.
Each amount is rounded to the cent, and the sale price, the tax and the total always add up. A shop's till may round differently.