How to work out a percentage
A percentage is just a fraction of 100. To find a percentage of any number, divide the percentage by 100 (turning it into a decimal), then multiply:
So 15% of 250 becomes 0.15 × 250 = 37.5. The same logic runs the other two calculations on this page: dividing one number by another and multiplying by 100 tells you what percentage it is, and comparing a change to its starting value tells you the percentage change.
The three percentage questions
Almost every real-world percentage problem is one of these three. Match your question to an example and use that mode above.
Working out percentages in your head
You can get most everyday answers quickly by building from easy percentages:
- 10%: move the decimal point one place left. 10% of 340 is 34.
- 1%: move it two places. 1% of 340 is 3.4.
- 5%: half of 10%. 5% of 340 is 17.
- Combine them: 23% of 400 is two lots of 10% (80) plus three lots of 1% (12), giving 92.
- Flip it when it helps: x% of y always equals y% of x. 4% of 75 feels hard, but 75% of 4 is obviously 3.
Frequently asked questions
How do I work out a percentage of a number?
Divide the percentage by 100, then multiply by the number. For example, 15% of 250 is (15 ÷ 100) × 250 = 37.5. A quick shortcut is to move the decimal point: 10% of 250 is 25, so 15% is 25 plus half of 25, which is 37.5.
How do I work out what percentage one number is of another?
Divide the first number by the second, then multiply by 100. For example, 30 as a percentage of 120 is (30 ÷ 120) × 100 = 25%.
What is the difference between percentage change and percentage difference?
Percentage change measures movement from a starting value to an end value, so it has a direction (increase or decrease) and uses the starting value as the base. Percentage difference compares two values with no direction, using the average of the two as the base. Use percentage change for prices over time, and percentage difference for comparing two alternatives.
How do I add a percentage to a number?
Multiply the number by 1 plus the percentage as a decimal. To add 20% to 80, multiply 80 × 1.20 = 96. To subtract 20%, multiply by 0.80 instead.
How do I work out percentages without a calculator?
Build from 10% and 1%. To find 10%, move the decimal point one place left. To find 1%, move it two places. Then combine: 23% of 400 is two lots of 10% (80) plus three lots of 1% (12), giving 92.