How to Calculate a Discount, Sale Price and Stacked Coupons
Work out a sale price and your savings for percent-off and dollar-off deals, why stacked discounts don't add up, and how to find an original price.
Published
Free tool: Discount Calculator"25% off, plus an extra 10% with this coupon." It sounds like 35% off, but it isn't. This guide shows how to calculate sale prices, savings and stacked discounts correctly, and how to work backward to an original price, using the free Discount Calculator.
Percent off
Sale price = original price × (1 − discount)
An $80 item at 25% off costs $80 × 0.75 = $60, saving $20.
Dollar off
Subtract the amount: $15 off an $80 item is $65. Buying 2 saves $30 in total.
Stacked discounts multiply
When a second discount is taken off the already reduced price, the discounts multiply rather than add:
- 25% off $80: $60
- An extra 10% off $60: $54
- Total saved: $26, which is 32.5% off, not 35%
Total discount = 1 − (1 − first) × (1 − second) = 1 − 0.75 × 0.90 = 32.5%.
Order doesn't matter for two percentage discounts, but it does when one is a dollar amount: $15 off and then 10% off isn't the same as 10% off and then $15 off.
Sales tax comes after
Sales tax is usually charged on the discounted price. At 8% tax, the $54 sale price becomes $58.32 at the register. See How to Calculate Sales Tax.
Finding the original price
If you paid $54 after 25% off and then an extra 10%, the original price was:
Original = sale price ÷ (1 − first) ÷ (1 − second) = $54 ÷ 0.90 ÷ 0.75 = $80
Is it a good deal?
- Compare the final price, not the percentage: 40% off an inflated "original" price can cost more than 20% off elsewhere.
- Watch thresholds: "spend $100, get $20 off" only saves money if you'd buy that much anyway.
- Check the unit price on bulk deals.
How to use the Discount Calculator
- Open the Discount Calculator.
- Choose what to calculate: the sale price or the original price.
- Enter the price and the discount, as a percentage or a dollar amount.
- Add an extra discount (a coupon taken off the sale price), the sales tax rate and the quantity if needed.
- Read the results: what you save, the total discount, the price per item and the total with tax, with a chart of what you pay vs what you save and a table of sale prices at common discounts.
Frequently asked questions
How do I calculate a percentage discount?
Multiply the price by (1 − discount). 25% off $80 is $80 × 0.75 = $60.
Are two discounts of 25% and 10% the same as 35% off?
No. The second discount applies to the reduced price, so the total is 32.5%: $80 becomes $60, then $54.
How do I find the original price before a discount?
Divide the sale price by (1 − discount). $60 after 25% off was $60 ÷ 0.75 = $80.