Find a percentage or work out the percentage given numbers and percent values. Use percent formulas to figure out percentages and unknowns in equations. Add or subtract a percentage from a number or solve the equations.
How to Calculate Percentages
There are many formulas for percentage problems. You can think of the most basic as X/Y = P x 100. The formulas below are all mathematical variations of this formula.
Let’s explore the three basic percentage problems. X and Y are numbers and P is the percentage:
- Find P percent of X
- Find what percent of X is Y
- Find X if P percent of it is Y
Read on to learn more about how to figure percentages.
1. How to calculate percentage of a number. Use the percentage formula: P% * X = Y
Example: What is 10% of 150?
- Convert the problem to an equation using the percentage formula: P% * X = Y
- P is 10%, X is 150, so the equation is 10% * 150 = Y
- Convert 10% to a decimal by removing the percent sign and dividing by 100: 10/100 = 0.10
- Substitute 0.10 for 10% in the equation: 10% * 150 = Y becomes 0.10 * 150 = Y
- Do the math: 0.10 * 150 = 15
- Y = 15
- So 10% of 150 is 15
- Double check your answer with the original question: What is 10% of 150? Multiply 0.10 * 150 = 15
2. How to find what percent of X is Y. Use the percentage formula: Y/X = P%
Example: What percent of 60 is 12?
- Convert the problem to an equation using the percentage formula: Y/X = P%
- X is 60, Y is 12, so the equation is 12/60 = P%
- Do the math: 12/60 = 0.20
- Important! The result will always be in decimal form, not percentage form. You need to multiply the result by 100 to get the percentage.
- Converting 0.20 to a percent: 0.20 * 100 = 20%
- So 20% of 60 is 12.
- Double check your answer with the original question: What percent of 60 is 12? 12/60 = 0.20, and multiplying by 100 to get percentage, 0.20 * 100 = 20%
3. How to find X if P percent of it is Y. Use the percentage formula Y/P% = X
Example: 25 is 20% of what number?
- Convert the problem to an equation using the percentage formula: Y/P% = X
- Y is 25, P% is 20, so the equation is 25/20% = X
- Convert the percentage to a decimal by dividing by 100.
- Converting 20% to a decimal: 20/100 = 0.20
- Substitute 0.20 for 20% in the equation: 25/0.20 = X
- Do the math: 25/0.20 = X
- X = 125
- So 25 is 20% of 125
- Double check your answer with the original question: 25 is 20% of what number? 25/0.20 = 125
Remember: How to convert a percentage to a decimal
- Remove the percentage sign and divide by 100
- 15.6% = 15.6/100 = 0.156
Remember: How to convert a decimal to a percentage
- Multiply by 100 and add a percentage sign
- 0.876 = 0.876 * 100 = 87.6%
There are nine variations on the three basic problems involving percentages. See if you can match your problem to one of the samples below. The problem formats match the input fields in the calculator above. Formulas and examples are included.
Find the change in percentage as an increase or decrease using the Percentage Change Calculator.
Solve decimal to percentage conversions with our Decimal to Percent Calculator.
Convert from percentage to decimals with the Percent to Decimal Calculator.
If you need to convert between fractions and percents see our Fraction to Percent Calculator, or our Percent to Fraction Calculator.
Weisstein, Eric W. “Percent.” From MathWorld – A Wolfram Web Resource.