Guides

How to calculate percentages

Percent means "per hundred". Four calculations cover almost everything.

1. A percent of a number

Number x percent / 100. Example: 20% of 150 = 150 x 20 / 100 = 30.

2. What percent is X of Y

X / Y x 100. Example: 45 is 45 / 300 x 100 = 15% of 300.

3. Increase or decrease by a percent

Increase: number x (1 + percent / 100). Decrease: number x (1 - percent / 100). Example: 80 raised by 25% is 80 x 1.25 = 100.

4. Percentage change

(new - old) / old x 100. Example: from 40 to 46 is (46 - 40) / 40 x 100 = +15%.

Mental shortcuts

• 10%: move the decimal point one place left. 10% of 85 is 8.5.
• 5%: half of 10%. 1%: move two places left.
• 20%: double 10%. 15%: 10% plus 5%.
• The percent of a number equals the number of that percent: 8% of 50 is the same as 50% of 8.

Try these with the percentage calculator.