Percentage calculator

How each answer is worked out

A percentage is a number out of 100, so 15% means 15 hundredths, or 0.15. Every question on this page uses that one idea.

What is X% of a number?

Divide the percentage by 100, then multiply. 15% of 80 is 0.15 × 80 = 12.

What percent is one number of another?

Divide the part by the whole, then multiply by 100. A test score of 45 out of 50 is 45 ÷ 50 = 0.9, which is 90%. This is the same sum as a marks percentage.

A number is X% of what?

Divide the number by the percentage as a decimal. If 12 is 15% of something, that something is 12 ÷ 0.15 = 80.

Adding or taking off a percentage

Work out the percentage of the starting number, then add it or take it away. 20% off a price of 50 is 50 − 10 = 40, the same as 50 × 0.8. Adding 10% sales tax to 40 gives 44. Note that taking 20% off and then adding 20% back does not return to the start: 40 plus 20% is 48, because the second 20% is of a smaller number.

Exact answers

The numbers are kept as exact fractions, so there are no rounding slips such as 0.30000000000000004. When an answer does not end, such as 1 out of 3 (33.333…%), it is rounded to 10 significant digits and marked "about". Round money answers to the cent yourself.