Discount Calculator
Updated · By the CalculatorDash editorial team · How we check our maths
Quick answer
Sale price = original price × (1 − discount). Stacked discounts multiply rather than add: 30% off followed by an extra 10% off is 37% off in total, not 40%. An $80 item at 30% + 10% off costs $50.40 before tax.
How this calculator works
A discount takes a percentage off the original price. When shops stack offers, such as a sale price plus a coupon, the second discount applies to the already-reduced price, so the combined discount is always less than the two percentages added together.
This calculator applies each discount in turn, then adds sales tax to the final price, which is how most tills work. In regions where tax is already included in shelf prices, leave tax at zero.
Retailers also use offers that are percentages in disguise. 'Buy two, get one free' is 33% off each item if you wanted three, but nothing if you only needed one. 'Spend $100, save $20' is a 20% discount only if you spend exactly $100. Converting every offer to a final price per item is the surest way to compare them.
The formula
- Sale price
- price × (1 − first discount) × (1 − extra discount)
- Total discount
- 1 − (1 − d1) × (1 − d2)
- Final price
- sale price × (1 + tax)
Worked example
An $80 jacket at 30% off is $56. An extra 10% coupon takes it to $50.40. You save $29.60, a total discount of 37%, not the 40% you'd get by adding the two.
Tips
- 01Compare the final price, not the headline percentage, when offers are stacked.
- 02'Buy one, get one half price' is a 25% discount on the pair.
- 03Check the original price history; inflated 'was' prices make discounts look bigger.
Frequently asked questions
How do I calculate a discount?
Multiply the price by the discount percentage and divide by 100 to get the saving, then subtract it from the price.
Do two discounts add up?
No. Each discount applies to the already-reduced price. 20% then 20% is 36% off, not 40%.
Is tax charged before or after a discount?
Usually after: tax is calculated on the discounted price. Manufacturer coupons can be an exception in some US states.
How do I find the original price from the sale price?
Divide the sale price by (1 − discount). $45 after 25% off was $60.