How to Calculate a Percentage: Three Easy Methods

Percentages appear everywhere: discounts, exam marks, tax, interest and statistics. Most problems fall into three types, and each has a simple rule.

1. Finding a percentage of a number

Multiply the number by the percentage and divide by 100. For example, 15 percent of 2,000 is 2,000 x 15 / 100 = 300.

2. Finding what percent one number is of another

Divide the part by the whole and multiply by 100. If you scored 42 out of 60, then 42 / 60 x 100 = 70 percent.

3. Percentage change

Subtract the old value from the new one, divide by the old value and multiply by 100. A price rising from 80 to 100 is a 25 percent increase, because 20 / 80 = 0.25.

A common trap

A rise of 25 percent is not undone by a fall of 25 percent. Going from 100 down to 80 is a 20 percent decrease, because the base number is different each time. Always divide by the starting value.

Quick mental tricks

• 10 percent: move the decimal point one place left.
• 5 percent: take half of 10 percent.
• 25 percent: divide by 4.

Percent versus percentage points

If an interest rate rises from 10 percent to 12 percent, it has gone up by 2 percentage points, but by 20 percent in relative terms, because 2 divided by 10 is 0.2. News stories and advertisements often mix these up, so check which one is meant.

Reverse percentages

Sometimes you know the final value and want the original. If a price is 600 after a 20 percent increase, divide by 1.20 to get the original: 600 / 1.20 = 500. For a decrease, divide by the remaining fraction instead, such as 0.80 for a 20 percent drop.

Percentages in daily life

• Exam marks: 450 out of 600 is 75 percent.
• Tax: a 10 percent tax on 5,000 adds 500.
• Fractions: 3/8 is 0.375, which is 37.5 percent.

Frequently asked questions

Can a percentage be more than 100?

Yes. 150 is 150 percent of 100. Values above 100 percent simply mean the part is larger than the whole you compare it with.

How do I turn a percentage into a decimal?

Divide by 100. So 35 percent becomes 0.35, and 4 percent becomes 0.04.

For any other numbers, use our Percentage Calculator, or work out sale prices with the Discount Calculator.