How to calculate a discount
Sale price = original price × (1 − discount ÷ 100)
Savings = original price − sale price
Savings = original price − sale price
An $80 item at 25% off costs $80 × 0.75 = $60, so you save $20. A quick trick for 20% off: take 10% by moving the decimal one place, then double it.
Stacked discounts do not add up
When a store takes 20% off and then an extra 10% off, the second discount applies to the already-reduced price. The result is 0.80 × 0.90 = 0.72 of the original price, a total discount of 28% instead of 30%. On an $80 item, you pay $57.60, not $56.
Working backwards to the original price
If you know the sale price and the discount, divide the sale price by (1 − discount). A jacket that costs $60 after 25% off originally sold for $60 ÷ 0.75 = $80.
Getting the best deal
- Compare the final price, not the percentage. 30% off a high starting price can still cost more than 15% off a lower one.
- Check the original price. Some "was" prices are inflated, so compare with other stores.
- Remember tax and shipping. Add sales tax to the sale price with the sales tax calculator, and include delivery costs when comparing.