Percentage Calculator

Calculate percentages of amounts, percentage change, reverse percentages and more. Free percentage calculator for GCSE and IGCSE maths.

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Find a Percentage of a Number

Calculate what X% of a number is

Percentage

Of this number

Enter values and click Calculate

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Study Guide

Percentage Essentials

Everything you need to learn percentages, broken down into simple, bite-sized cards.

1. What is a Percentage?

A percentage is a number out of 100. The word comes from per centum, meaning "out of one hundred". So 45% means 45 out of 100.

$45\% = \frac{45}{100} = 0.45$

Quick Conversion

Every percentage has a fraction and decimal twin: 45% = 45/100 = 0.45. Learning the common ones by heart (25%, 50%, 75%) will save you loads of time in the exam!

2. How to Convert Fractions into Percentages?

To turn a fraction into a percentage, divide the top by the bottom, then multiply by 100. This works for any fraction.

$\frac{3}{5} = 3 \div 5 = 0.6 \rightarrow 60\%$

Common Ones to Remember

$\frac{1}{2}$ = 50%
$\frac{1}{4}$ = 25%
$\frac{1}{5}$ = 20%
$\frac{3}{4}$ = 75%

3. How to Find a Percentage of a Number?

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To find a percentage of a number, divide the percentage by 100 to write it as a decimal, then multiply by the number.

$30\% \text{ of } 240 = 0.3 \times 240 = 72$

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4. How to Find a Percentage Increase or Decrease?

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To increase a value by a percentage, multiply by (1 + rate). To decrease, multiply by (1 - rate). Convert the percentage to a decimal first.

$100 \times (1 + 20\%) = 100 \times 1.2 = 120$

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5. How to Calculate Percentage Change?

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Percentage change compares an original value to a new value. To find it: subtract the original from the new, divide by the original, then multiply by 100.

$\frac{60 - 50}{50} \times 100 = 20\%\text{ increase}$

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6. How to Find a Reverse Percentage?

A reverse percentage finds the original value before a percentage change. If the price increased by 20%, the multiplier is 1.20. To reverse it, divide by that multiplier.

$\text{Before 20\% increase: } 120 \div 1.2 = 100$

Remember

To reverse a percentage, always divide by the multiplier. Never subtract the percentage from the new value!

Practice

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$\text{What is } 15\% \text{ of } 80 \text{ ?}$

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