How to calculate percentages
A percentage is just a number out of 100. The word "percent" literally means "per hundred", so 20% is the same as 20 out of 100, or the fraction 20/100 = 0.2. Most everyday percentage questions fall into the three types on this page.
Percent of a number
To find a percent of a number, multiply the number by the percent and divide by 100. For example, 20% of 150 is 150 × 20 ÷ 100 = 30. This is handy for tips, taxes and discounts.
What percent one number is of another
Divide the part by the whole and multiply by 100. If you scored 30 out of 150, that is 30 ÷ 150 × 100 = 20%.
Percentage increase and decrease
Take the difference between the new and old values, divide by the old value, then multiply by 100. A price rising from 80 to 100 is a (100 − 80) ÷ 80 × 100 = 25% increase; falling from 100 to 80 is a 20% decrease.