How to use the Percentage Calculator
- Enter the percentage you want, for example 15.
- Enter the number you want to take the percentage of.
- Read the result. It updates as you type.
Formula used
X% of Y = (X ÷ 100) × Y.
Worked example
Here is the Percentage Calculator worked through with the example values shown above, so you can check each step by hand.
| Inputs | |
|---|---|
| Percentage | 15 % |
| Of the number | 200 |
| Result | |
| Result | 30 |
How to calculate a percentage of a number
Divide the percentage by 100 and multiply by the number. 15% of 200 is 0.15 × 200 = 30. 18% of 2,500 is 0.18 × 2,500 = 450, and 5% of 80 is 0.05 × 80 = 4.
A mental shortcut is to find 10% by moving the decimal point one place, then build up from there. 10% of 80 is 8, so 5% is half of that, which is 4.
Adding and subtracting a percentage
To increase a number by a percentage, multiply it by 1 plus the percentage as a decimal. Adding 10% to 500 gives 500 × 1.10 = 550. To decrease it, multiply by 1 minus the percentage, so taking 10% off 500 gives 500 × 0.90 = 450.
Be careful when you apply percentages one after another. A 10% increase followed by a 10% decrease does not return to the start: 100 becomes 110, and 10% off 110 is 99.
Where percentages are used
Common uses include working out GST on a bill, a discount in a sale, the interest on a deposit, a salary hike, a service charge and exam marks. If you need to find what percent one number is of another, use the What Percent calculator. If you need the change between an old and a new value, use the Percentage Change calculator.
Mental shortcuts for percentages
To find 10% of a number, move the decimal point one place left. 1% is two places left. From there you can build most percentages: 20% is double 10%, 5% is half of 10%, and 15% is 10% plus 5%. So 15% of 80 is 8 + 4 = 12.
To find 50% halve the number, 25% halve it twice and 75% is 25% subtracted from the whole. To reverse a percentage, divide: if 20% of a number is 30, the number is 30 ÷ 0.20 = 150. Percentages of percentages multiply, so 20% of 50% is 10%.
Frequently asked questions
How do I find a percentage of a number?
Divide the percentage by 100 and multiply by the number. For example, 15% of 200 is 0.15 × 200 = 30.
How do I add a percentage to a number?
Multiply the number by (1 + percentage ÷ 100). To add 10% to 500, calculate 500 × 1.10 = 550.
How do I subtract a percentage from a number?
Multiply the number by (1 − percentage ÷ 100). To take 20% off 1,000, calculate 1,000 × 0.80 = 800.
What is 10% of a number the quick way?
Move the decimal point one place to the left. 10% of 2,500 is 250. You can then double it for 20% or halve it for 5%.
Can a percentage be more than 100?
Yes. 150% of 40 is 60, which is one and a half times 40. Percentages above 100 describe amounts larger than the original.
Why does a 10% increase followed by a 10% decrease not give the original number?
Because the second percentage is taken from a different base. After a 10% increase, 100 becomes 110, and a 10% decrease of 110 is 11, which leaves 99.
How do I find the original number if I know a percentage of it?
Divide the known amount by the percentage as a decimal. If 20% of a number is 30, the number is 30 ÷ 0.20 = 150.
This calculator gives estimates for information only. Actual figures from a bank, employer, tax authority or doctor may differ. It is not financial, tax, legal or medical advice.