How percentages are calculated
Per cent means per hundred, so every percentage is a fraction of 100.
X% of Y = X ÷ 100 × Y · X as % of Y = X ÷ Y × 100
- X% of Y: divide X by 100 to get a decimal, then multiply by Y. 15% of 200 is 0.15 × 200 = 30.
- X is what % of Y: divide X by Y, then multiply by 100. 30 ÷ 200 × 100 = 15%.
- Y plus X%: work out X% of Y and add it to Y. 200 + 30 = 230, the same as 200 × 1.15.
- Y minus X%: work out X% of Y and take it away. 200 − 30 = 170, the same as 200 × 0.85.
- The total in the second mode cannot be 0, because you cannot divide by zero.
Worked example — 15% of 200 is 15 ÷ 100 × 200 = 30. Adding it gives 230 and taking it off gives 170. Going the other way, 30 is 15% of 200.
Common percentages
| Percentage | Of | 10% of 50 |
|---|---|---|
| 10% | 50 | 5 |
| 15% | 80 | 12 |
| 20% | 150 | 30 |
| 25% | 200 | 50 |
| 30% | 1,000 | 300 |
| 12.5% | 64 | 8 |
Swipe the table sideways to see the rest.
Each row works out X% of Y.
Things to consider
- For 10%, move the decimal point one place left. 10% of 85 is 8.5.
- X% of Y always equals Y% of X, so 8% of 50 is the same as 50% of 8, which is 4.
- To add GST of 10%, use Y plus X%. To remove it from a GST-inclusive price, divide by 1.1 instead.
- A rise then a fall of the same percentage does not return you to the start.
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 0.15 × 200 = 30.
How do I work out what percent one number is of another?
Divide the part by the total and multiply by 100. 30 out of 200 is 30 ÷ 200 × 100 = 15%.
How do I add a percentage to a number?
Work out the percentage and add it, or multiply by 1 plus the percentage as a decimal. 200 plus 15% is 200 × 1.15 = 230.
How do I take a percentage off?
Work out the percentage and subtract it, or multiply by 1 minus the decimal. 200 minus 15% is 200 × 0.85 = 170.
Is X% of Y the same as Y% of X?
Yes. Both equal X × Y ÷ 100, so 4% of 75 and 75% of 4 are both 3.
How do I find the percentage change between two numbers?
For the change between two numbers, use the Percentage Increase and Change Calculator. It shows the rise or fall as a percentage.
Results are estimates for general information only, not financial, medical or professional advice.