How to Calculate a Percentage

How Do I Calculate a Percentage of a Number?

To find a percentage of a number, multiply the number by the decimal form of the percentage. For 15% of 200, convert 15% to 0.15 and multiply: 200 times 0.15 equals 30. On a calculator you can also press the percentage key after multiplying, but converting to a decimal and multiplying works on every calculator.

How Do I Find What Percent One Number Is of Another?

Divide the part by the whole and multiply by 100. If you scored 42 out of 60 on a test, divide 42 by 60 to get 0.7, then multiply by 100 to get 70%. On a calculator the buttons are 42, divide, 60, multiply, 100, equals. The result is the percentage of the total that your score represents.

How Do I Calculate Percentage Increase or Decrease?

Subtract the original value from the new value, divide by the original value, and multiply by 100. If a price rises from $50 to $60, the difference is 10, and 10 divided by 50 times 100 equals a 20% increase. If the new value is lower than the original, the result is a percentage decrease.

How Do I Calculate a Percentage on a Calculator?

Most calculators handle the three common percentage problems with basic operations. To find what percent one number is of another, divide and multiply by 100. To find a percentage of a number, multiply by the decimal form. To find percent change, subtract, divide by the original, and multiply by 100. You never need a special percentage button.

Common Percentage Mistakes to Avoid

The most common mistake is multiplying by the percentage instead of its decimal form, which gives an answer 100 times too large. Another common error is dividing the change by the new value instead of the original value when finding percent change. Always identify the original value first before you divide.