Choose the value you are missing, type the other two (the percent goes in as a plain number, so 15 means 15%), and select “Calculate”. If you have a fraction, use fraction to percent; this page works from the relationship between part, whole and percent.
Worked example, 15% of 80
In a survey, 80 people respond and 15% prefer tea. How many is that?
- Write the percent as a fraction. 15% means 15 out of every 100, or 15/100.
- Multiply by the whole. 15/100 × 80 = 1200/100.
- Simplify. 1200/100 = 12.
That is 12 people.
Check. 10% of 80 is 8 and 5% is 4, and 8 + 4 = 12.
Which value do you have?
Every percent problem has three values and one is missing. The table shows which mode to choose for what you know, using the numbers from the example to show it is the same relationship each time.
| You have | You want | Calculation |
|---|---|---|
| Percent and whole | The part | 15% of 80 = 15/100 × 80 = 12 |
| Part and whole | The percent | 12 out of 80 = 12/80 × 100 = 15% |
| Part and percent | The whole | 12 is 15%, so 12 ÷ (15/100) = 80 |
In the second mode the whole always goes in the second field; if you swap them, you calculate what percent 80 is of 12, which is a different question.
How the result appears
The calculator works with fractions and does not round. When the result is not a whole number, you see it as a reduced fraction and, where it applies, as a decimal: 7/8 of a whole appears as 87.5%, and 2/3 as 200/3%, which as a decimal is 66.6̅%. If you need a fixed number of decimal places, round at the end and note that it is an approximation; with 66.67 the error is also 1/300 of a percentage point.
Here decimals use a point and the % sign is attached to the number, as in 35%.
The tool only solves the calculation with part, whole and percent; it does not handle compound interest, payments or taxes, which need more information.
Other pages for working with percents
To go from a percent to a fraction, use percent to fraction. When both amounts are of the same kind and you want the fraction one is of the other, use what fraction. If you want a fraction of an amount, such as 3/4 of 80, there is fraction of a number, and for different proportional quantities, the rule of three.
Sources
OpenStax Prealgebra 2e explains how to solve general applications of percent by writing amount = percent × base and solving for the unknown (accessed October 17, 2026).
Frequently asked questions
How do I calculate a percent increase?
Find the percent and add it to the starting amount, or multiply by 1 plus the percent as a decimal. To raise $250 by 8%, the increase is $20 and the new price is 250 × 1.08 = $270. The result is 108% of the original price.
How do I calculate a discount?
Find the percent of the price and subtract it, or calculate the percent you pay directly. With 30% off $140, the discount is $42 and you pay $98, which is 70% of the price. Both routes always give the same answer.
Can a percent be greater than 100%?
Yes. A percent above 100% means the part is larger than the base. 150% of 18 is 1.5 × 18 = 27. It is common when comparing with an earlier value: if something goes from 18 to 27, the new value is 150% of the starting one.
What is the difference between percentage points and percent?
Percentage points subtract two percents; percent change compares with the starting value. If a rate goes from 6% to 9%, it rises 3 percentage points, but the relative change is 9/6 = 1.5, an increase of 50%.
How do I remove sales tax from a price that includes it?
Divide the price by 1 plus the tax rate as a decimal; subtracting the percent gives the wrong result. With an 8% rate, a price of $216 has a pre-tax amount of 216 ÷ 1.08 = $200. Rates vary by place, and the article on removing tax from a price covers more cases.