Percentage Calculator
Marks, scores and survey results: enter the part and the total. You can also find a percent of a number, work out what percent one number is of another, find the whole from a part, or find a percent of a percent. Every answer shows the steps. It runs in your browser, so nothing you enter is stored.
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Result
Steps
Quick answer
A percentage is a part out of 100. To find a percent of a number, multiply the number by the percent and divide by 100. For example, 15 percent of 200 is 30. To go the other way, divide the part by the whole and multiply by 100. For example, 70 marks out of 100 is 70 percent, and 42 out of 50 is 84 percent. For several subjects together, use the marks percentage calculator.
Use the calculator above for the four most common jobs: finding a percent of a number, finding what percent one number is of another (like marks out of a total), finding the whole from a part, and finding a percent of a percent.
How to calculate a percentage
Find a percent of a number
Here we find 15 percent of 200.
- Turn the percent into a decimal by dividing by 100. 15 divided by 100 is 0.15.
- Multiply the decimal by the number. 0.15 times 200 is 30.
Find what percent one number is of another
Here we find what percent 30 is of 200.
- Divide the part by the whole. 30 divided by 200 is 0.15.
- Multiply by 100. 0.15 times 100 is 15 percent.
Find the whole from a part and a percent
Here 30 is 15 percent of a number.
- Turn the percent into a decimal. 15 percent is 0.15.
- Divide the part by the decimal. 30 divided by 0.15 is 200.
Percentage formulas
| What you want | Formula | Example |
|---|---|---|
| X percent of Y | Y x X / 100 | 15% of 200 = 30 |
| What percent X is of Y | X / Y x 100 | 30 of 200 = 15% |
| The whole from a part | X / (P / 100) | 30 is 15% of 200 |
| A percent of a percent | A x B / 100 | 20% of 50% = 10% |
The part is the piece you are looking at, and the whole is the amount it belongs to. Most mistakes come from mixing up which number is the part and which is the whole.
Percentage examples
| Situation | Question | Answer |
|---|---|---|
| Tip | What is 18% of 45? | 8.1 |
| Test mark | 42 out of 50 is what percent? | 84% |
| Sale | 25% off 80 | 20 off, so you pay 60 |
| Sales tax | 8% tax on 60 | 4.8 tax, so the total is 64.8 |
| Savings | 600 is 12% of what? | 5,000 |
| Survey | 18 of 240 people | 7.5% |
Notice that the question decides the formula. A tip and a tax both ask for a percent of a number. A test mark and a survey ask what percent one number is of another. Savings asks for the whole.
What is a percentage?
The word percent comes from the Latin for out of a hundred. 1 percent is one part out of 100, 50 percent is 50 parts out of 100, which is one half, and 100 percent is the whole thing. A percentage is just a way to write a fraction with 100 on the bottom, so 3/4 is 75/100, or 75 percent. This makes it easy to compare amounts of different sizes, such as 9 out of 12 and 15 out of 20. Both are 75 percent.
Percent vs percentage points
These two are easy to mix up. Percent is a share of a base value. Percentage points are the plain gap between two percentages. If an interest rate moves from 4 percent to 5 percent, it rose by 1 percentage point. Compared with where it started, it rose by 25 percent, because 1 is a quarter of 4.
Newspapers use both, so check which one a headline means. For the full explanation, use our percentage point calculator. To compare two values that have no clear start, use the percentage difference calculator.
Everyday uses of percentages
Tips and tax. A tip of 18 percent on a 45 bill is 8.10. Sales tax of 8 percent on 60 adds 4.80. Our tip calculator and sales tax calculator do these in one step.
Discounts. A 25 percent discount on 80 takes 20 off the price. Use the discount calculator to see the sale price and the saving.
Marks and grades. A score of 42 out of 50 is 84 percent. The marks percentage calculator handles several subjects at once.
Growth and change. Prices, salaries and website visitors are all compared with percentages. For that, use the percentage increase calculator or the percentage decrease calculator.
Working out percentages in your head
Start with 10 percent. Move the decimal point one place to the left. 10 percent of 80 is 8. Half of that is 5 percent, which is 4. Add the two for 15 percent, which is 12.
| Percent | Quick way | Of 80 |
|---|---|---|
| 1% | Divide by 100 | 0.8 |
| 5% | Half of 10% | 4 |
| 10% | Divide by 10 | 8 |
| 20% | Double 10% | 16 |
| 25% | A quarter | 20 |
| 50% | Half | 40 |
| 75% | Three quarters | 60 |
Common mistakes
Mixing up the part and the whole. In 30 out of 200, the part is 30 and the whole is 200. Dividing the other way gives 6.67, which is not the answer you want.
Adding and taking off the same percent. A 20 percent rise and then a 20 percent fall does not bring you back. 100 becomes 120, then 96.
Forgetting to divide by 100. 15 percent is 0.15 in a calculation, not 15.
Taking a percent off the wrong value. To undo a 15 percent increase, divide by 1.15. Do not take 15 percent off the new price.
About this calculator
The calculator uses the standard formulas shown above and rounds results, and the numbers shown in the result line, to four decimal places at most (trailing zeros are dropped). Load example fills the open calculator with 500 out of 800, 15% of 200, 30 is 15% of 200, or 20% of 50%. It works with whole numbers and decimals, accepts commas in large numbers, and runs in your browser, so nothing you enter is stored or sent.
Frequently asked questions
How do I calculate a percentage of a number?
Multiply the number by the percentage, then divide by 100. To find 15 percent of 200, multiply 200 by 15 to get 3,000, then divide by 100 to get 30. You can also turn the percent into a decimal first: 15 percent is 0.15, and 0.15 times 200 is 30.
How do I find what percent one number is of another?
Divide the part by the whole, then multiply by 100. If 30 out of 200 people said yes, divide 30 by 200 to get 0.15, then multiply by 100. The answer is 15 percent.
How do I find the whole when I know the part and the percent?
Divide the part by the percent written as a decimal. If 30 is 15 percent of a number, divide 30 by 0.15. The whole number is 200. You can check it by finding 15 percent of 200, which is 30.
How do I work out my marks as a percentage?
Divide the marks you got by the total marks, then multiply by 100. If you scored 70 out of 100, the answer is 70 percent. If you scored 42 out of 50, divide 42 by 50 to get 0.84, then multiply by 100 to get 84 percent. The marks percentage calculator can add several subjects together.
What is 1 percent of a number?
Divide the number by 100. 1 percent of 200 is 2. Once you know 1 percent, multiply it by any percent to get the answer, so 15 percent of 200 is 15 times 2, which is 30.
How do I find a percentage of a percentage?
Change both percentages to decimals and multiply them. 20 percent of 50 percent is 0.2 times 0.5, which is 0.1, or 10 percent. This is useful for things like a 20 percent discount on a price that already has 50 percent off.
How do I turn a percentage into a decimal?
Divide it by 100, which moves the decimal point two places to the left. 15 percent becomes 0.15, and 7.5 percent becomes 0.075. To go back, multiply the decimal by 100.
Can a percentage be more than 100?
Yes. 150 is 150 percent of 100, and a price that doubles has grown by 100 percent. A part of something cannot be more than 100 percent of that same thing, but a comparison or a growth figure can.
How do I calculate percentage change between two numbers?
Subtract the old value from the new value, divide by the old value and multiply by 100. The percentage increase and percentage decrease calculators do this with steps, and the percentage difference calculator compares two values that have no order.
What is the difference between percent and percentage points?
Percent is a share of a base value. Percentage points are the plain gap between two percentages. A rate that moves from 4 percent to 5 percent rose by 1 percentage point, but it grew by 25 percent compared with where it started.
Why do a 20 percent increase and a 20 percent decrease not cancel out?
Because each percent applies to a different base. 100 plus 20 percent is 120, but 20 percent of 120 is 24, so taking it off gives 96, not 100. To undo a 20 percent increase you need a decrease of 16.67 percent.
How can I work out percentages in my head?
Start with 10 percent by moving the decimal point one place to the left. 10 percent of 80 is 8. Half of that is 5 percent, which is 4. Add them for 15 percent, which is 12. Doubling 10 percent gives 20 percent, and 50 percent is simply half.
About the author
Umar Khan is a PhD student in engineering at NTNU. He writes and checks the maths on UtilMora.
For information only, not professional advice.
Written by Umar Khan. Last updated: November 2, 2026.