Percentage Calculator
Free to use. Runs in your browser: your files and text are not uploaded.
Three percentage calculations in one tool. Choose the question, type two numbers, and read the answer.
How to use it
- Choose what you want to work out.
- Type X and Y. The answer updates as you type.
The three calculations
What is X% of Y? Formula: X ÷ 100 × Y. Example: a 15% tip on a bill of 200 is 15 ÷ 100 × 200 = 30.
X is what percent of Y? Formula: X ÷ Y × 100. Example: 30 marks out of 200 is 30 ÷ 200 × 100 = 15%.
Percentage change from X to Y Formula: (Y − X) ÷ X × 100. Example: a price that goes from 80 to 100 has risen by (100 − 80) ÷ 80 × 100 = 25%. From 100 down to 80 is a fall of 20%, because the starting amount is now 100.
Percent and percentage points
When a rate moves from 4% to 5%, it has risen by 1 percentage point. As a percentage change it has risen by 25%, since 1 is a quarter of 4. News reports often mix the two, so check which one is meant.
Quick mental checks
- 10% of a number: move the decimal point one place left. 10% of 250 is 25.
- 5% is half of 10%. 1% is a tenth of 10%.
- X% of Y equals Y% of X. So 8% of 50 is the same as 50% of 8, which is 4.
Limits
- Percentage change needs a starting value that is not zero. A change from 0 has no percentage.
- When the starting value is negative, the tool divides by its size without the minus sign, so a move from −50 to −25 shows as a 50% increase.
Frequently asked questions
How do I calculate a percentage of a number?
Divide the percentage by 100 and multiply by the number. 15% of 200 is 15 ÷ 100 × 200 = 30.
How do I calculate percentage increase?
Subtract the old value from the new one, divide by the old value, and multiply by 100. From 80 to 100 is (100 − 80) ÷ 80 × 100 = 25%.
Why is a 50% rise followed by a 50% fall not back where it started?
The two percentages are taken from different starting amounts. 100 plus 50% is 150. Then 50% of 150 is 75, which leaves 75.