How to Calculate Percentages and Discounts
Simple methods and worked examples for sales, extra discounts, tax and percentage change.
Percentages appear in every sale, salary slip and bill. Here are the four calculations you will use most often, with examples you can check against the calculators on this site.
1. A percentage of a number
Multiply the number by the percent and divide by 100. For example, 15% of 2,400 is 2,400 × 15 ÷ 100 = 360.
2. A discount
A 20% discount on a 5,000 item takes off 5,000 × 20 ÷ 100 = 1,000. You pay 4,000.
3. An extra discount on top of a discount
Two discounts do not simply add up. The second one applies to the price that is already reduced. Take 20% off 5,000 to get 4,000, then take 10% off that: 4,000 × 0.90 = 3,600. The total saving is 1,400, which is 28% of 5,000, not 30%.
4. Percentage change
Percentage change = (new value − old value) ÷ old value × 100. If a price rises from 80 to 100, the change is 20 ÷ 80 × 100 = 25%. If it then falls from 100 back to 80, the change is −20%. The two numbers differ because the starting value is different.
Adding tax
Work out the discounted price first, then add tax to it. A price of 4,000 with 10% tax costs 4,000 × 1.10 = 4,400.
Using the calculators
Open the Discount Calculator, enter the original price, the discount, an optional extra discount and an optional tax rate. The final price and the amount you save update as you type. For a quick share of a number, use the Percentage Calculator.
Tip
Before buying, compare the final price, not just the size of the discount. A bigger percentage off a higher starting price can still cost more.