Percentages made easy: discounts, tips and tax
Percentages come up constantly: a sale price, a tip, a tax, a test score. Almost every real question is one of three types, and once you know them the maths is quick. Here is the practical version, no jargon.
A percent of a number
To find a percent of a number, multiply the number by the percent and divide by 100. A 20% tip on a 50 bill is 50 × 20 ÷ 100 = 10. The same method handles tax and discounts: 10% tax on 200 adds 20, and a 30% discount on a 50 item saves 15, so you pay 35.
What percent one number is of another
To see what percent one number is of another, divide the part by the whole and multiply by 100. If you scored 45 out of 60, that is 45 ÷ 60 × 100 = 75%. This is how you turn a fraction or a result into a percentage.
Percentage increase and decrease
For a change, take the difference between the new and old values, divide by the old value, and multiply by 100. A price rising from 80 to 100 is a 25% increase; falling from 100 to 80 is a 20% decrease — the percentages differ because the starting value is different each time. To add or subtract a percent quickly, multiply by (1 + percent/100) or (1 − percent/100).
Try it: run these in one click with the free CalcBloom percentage calculator →