Three percentage questions: X% of Y, X is what percent of Y, and X is Y% of what number.
Enter the values to see the result here.
Formula
The three modes are one relationship, part=100p×whole, solved for a different unknown.
X% of Y=100XYX is what % of Y=YX×100X is Y% of W:W=Y/100X
Worked example
15% of 200: 0.15×200=30.
30 is what percent of 240: 30/240×100=12.5%.
45 is 18% of what: 45/0.18=250.
A quick check of the last one: 18% of 250 is 0.18×250=45, so the answer is consistent.
Common mistakes
Dividing by the part instead of the whole when finding a percentage. “30 of 240” divides by 240, not by 30.
Confusing “X% of Y” with “Y% of X”. They give the same number, but only because multiplication commutes; the meaning differs.
Entering 0.15 where the field wants 15.
Using a percentage of a percentage without converting: 20% of 50% is 10% of the original.
Frequently asked questions
How do I work out a percentage in my head?
Find 10% by moving the decimal one place, then build up. For 15% of 80, 10% is 8 and 5% is half of that (4), so 12. For 20%, double the 10% figure.
What is the difference between "X% of Y" and "X is what % of Y"?
The first starts from a percentage and finds a quantity; the second starts from two quantities and finds the percentage. Pick the sentence that matches your problem.
Can a percentage be more than 100?
Yes. 150 is 150% of 100. Values above 100% simply mean the part is bigger than the reference, as with growth of more than double.
How do I add or take off a percentage?
To add 20%, multiply by 1.20. To subtract 20%, multiply by 0.80. For tax and discounts use the dedicated calculators.