How to Calculate Percentages (the Easy Way)

Find a percentage of a number, a percentage increase or decrease, and what percent one number is of another — with quick mental tricks.

A percentage is just a fraction of one hundred, so "per cent" literally means "per hundred". Once that clicks, most percentage questions become one short multiplication or division.

Finding X% of a number

Multiply the number by the percentage divided by 100. So 20% of 150 is 150 × 0.20 = 30. A quick trick: 10% is the number with the decimal point moved one place left, and you can build others from it — 5% is half of 10%, 20% is double. The percentage calculator does any of these instantly.

What percent is A of B?

Divide A by B and multiply by 100. If 30 out of 150 people said yes, that is 30 ÷ 150 × 100 = 20%. This is how you turn a score, a share or a conversion rate into a percentage.

Percentage increase and decrease

Subtract the old value from the new, divide by the old, and multiply by 100. Going from 40 to 50 is (50 − 40) ÷ 40 × 100 = 25% increase. Going from 50 to 40 is a 20% decrease — note the two are not the same, because the starting point differs.

Percent vs percentage points

These are easy to confuse. Moving from 10% to 12% is a rise of two percentage points, but a 20% increase in relative terms. Being clear which one you mean avoids a lot of confusion in reports and news.

Everyday uses

The same maths powers discounts, tips, tax, interest and test scores. If you can find a percentage of a number and a percentage change, you can handle almost any everyday money or data question.