Sales, coupons and promo codes are designed to make you feel you are getting a bargain. Knowing how to calculate discounts yourself helps you check whether a deal is as good as it sounds and compare offers quickly. The formulas are short, and with a few examples you will be able to do most of the work in your head.
The basic discount formula
To find the amount you save, multiply the original price by the discount percentage and divide by 100. Then subtract it from the original price.
- Savings = original price × discount ÷ 100
- Sale price = original price − savings
There is an even faster route: multiply the original price by (1 − discount as a decimal). For 25% off, multiply by 0.75.
Example: A jacket costs 120 and is 25% off. Savings: 120 × 25 ÷ 100 = 30. Sale price: 120 − 30 = 90. Or directly: 120 × 0.75 = 90.
Mental math shortcuts
- 10% off: move the decimal point one place left and subtract. On 85, 10% is 8.50, so the price is 76.50.
- 20% off: find 10%, double it, then subtract.
- 25% off: take away a quarter of the price.
- 50% off: halve it.
- 15% off: 10% plus half of 10%.
Stacked discounts: why they do not simply add
Many stores offer something like "30% off, plus an extra 10% with this code". It is tempting to add them and expect 40% off. In reality, the second discount applies to the price already reduced by the first.
Example: An item costs 200. After 30% off the price is 140. An extra 10% off 140 is 14, so you pay 126. The combined discount is 37%, not 40%. The shortcut is to multiply the factors: 0.70 × 0.90 = 0.63, so you pay 63% of the original price.
Another common offer is 25% off followed by 10% off. The total is 1 − (0.75 × 0.90) = 1 − 0.675 = 32.5%.
Finding the original price
If a sale price and discount are known but not the original, divide the sale price by (1 − discount). A coat costing 90 after 25% off was originally 90 ÷ 0.75 = 120. A common mistake is to add 25% back to 90, which gives 112.50, an incorrect answer.
Finding the discount percentage
If the original price was 80 and the sale price is 60, the savings are 20. The discount percentage is 20 ÷ 80 × 100 = 25%.
Compare deals correctly
Which is better: 30% off a 90 item, or 20% off a 100 item? The first costs 63 and the second costs 80. Always compare final prices, not just the percentages. Also compare unit prices when quantities differ: "buy two, get 20% off" is only a good deal if you really need two.
Be careful with tricks
- Inflated "original" prices. A store may raise the regular price before a sale. Compare with other shops or a price history tool.
- Taxes and shipping. Check whether the discount applies before or after tax, and whether shipping costs cancel the saving.
- Minimum purchase conditions. A discount that requires spending more than you planned may increase your total spending.
- Pressure tactics. "Only today" labels are meant to speed up your decision. If you would not buy it at full price, the discount does not make it a need.
Calculate it in seconds
Use our Discount Calculator to enter the original price and one or two discounts, and it shows your final price, how much you save and the true total discount. Need to add or remove tax afterwards? Try the Sales Tax & VAT Calculator.