Percentage calculator for the three everyday questions
Choose the question and enter X and Y. 15% of 200 is 30; 30 is 15% of 200; and if 30 is 15% of a number, that number is 200. Percent means per hundred, so every form is a multiplication or division by 100.
Inputs used by this calculator
Percentage Calculator uses the fields below. The starting values reproduce the page example; replace them with values from the same units and time period before using the result.
| Input | Starting example | Accepted value | How it is used |
|---|---|---|---|
| Question | What is X% of Y? | What is X% of Y? · X is what percent of Y? · X is Y% of what? | Chooses which Percentage Calculator method or unknown the engine evaluates. |
| X | 15 | Any finite number supported by the formula | Supplies the x quantity used by the published equation or result breakdown. |
| Y | 200 | Any finite number supported by the formula | Supplies the y quantity used by the published equation or result breakdown. |
The three percentage questions
Almost every everyday percentage problem is one of three questions. What is 15% of 200? (the part). 30 is what percent of 200? (the percent). 30 is 15% of what number? (the whole). They all come from one relationship, part = percent ÷ 100 × whole, solved for a different unknown.
part = percent ÷ 100 × wholepercent = part ÷ whole × 100whole = part ÷ (percent ÷ 100)What percent means
Percent means “per hundred”. 15% is 15 per 100, or 0.15 as a decimal. Converting a percent to a decimal moves the decimal point two places to the left; converting back moves it two places to the right. The table below lists common percents with their decimal and fraction forms.
Quick mental math
10% of a number moves its decimal point one place left: 10% of 84 is 8.4. From there, 5% is half of that and 20% is double. For a 15% or 20% restaurant tip, find 10% and adjust. Percentages over 100 are fine: 150% of 40 is 60.
Percent versus percentage points
When a rate moves from 4% to 5%, it rose by one percentage point, but by 25 percent of its old value. News stories and loan offers mix the two, so check which one is meant. For changes between an old and a new value, the Percentage Change Calculator gives the percent increase or decrease.
Choosing the right whole
The most common mistake is dividing by the wrong number. “What percent of the budget is rent?” divides rent by the budget, not the other way around. Say the question out loud with “of”: the number after “of” is the whole.
Negative and very large values
Percentages can be negative, such as a −3% return, and results can exceed the whole when the percent is above 100. The only impossible case is dividing by zero: a percent of a zero whole is undefined, and a part cannot be 0% of anything but zero.
Common percentages as decimals and fractions
| Percent | Decimal | Fraction |
|---|---|---|
| 1% | 0.01 | 1/100 |
| 5% | 0.05 | 1/20 |
| 10% | 0.1 | 1/10 |
| 12.5% | 0.125 | 1/8 |
| 20% | 0.2 | 1/5 |
| 25% | 0.25 | 1/4 |
| 33⅓% | 0.333… | 1/3 |
| 50% | 0.5 | 1/2 |
| 75% | 0.75 | 3/4 |
| 100% | 1 | 1/1 |
| 150% | 1.5 | 3/2 |
Frequently asked questions
How do I calculate a percentage of a number?
Multiply the number by the percent and divide by 100: 15% of 200 = 15 × 200 ÷ 100 = 30.
How do I find what percent one number is of another?
Divide the part by the whole and multiply by 100: 30 ÷ 200 × 100 = 15%.
How do I find the whole from a part and a percent?
Divide the part by the percent as a decimal: 30 ÷ 0.15 = 200.
What is 20% of 50?
10. Ten percent of 50 is 5, and 20% is twice that.
Can a percentage be more than 100?
Yes. 150% of a number is one and a half times the number.
What is the difference between percent and percentage points?
Percentage points measure the difference between two percentages; percent measures a change relative to the starting value.
How do I work out a percent increase?
Use the Percentage Change Calculator: (new − old) ÷ old × 100.
What to keep in mind
Percentages can be negative or greater than 100. Use percentage change to compare an old and a new value.
Results are rounded for display in US format, with money in dollars and cents; CSV exports keep full calculation precision. This is a calculation summary, not an official certificate.