Percentage Calculator
Three everyday percentage questions, answered with the calculation shown. Choose a mode and enter your numbers.
Calculate a percentage of a number
Choose “What is X% of Y?”. Enter the percentage and the total. For example, 20% of 150 is 30, calculated as 20 ÷ 100 × 150. If a price is reduced by 20%, subtract this result from the original price: 150 − 30 = 120.
Find what percentage one amount represents
Choose “X is what % of Y?”. The first amount is divided by the second and multiplied by 100. For example, 18 out of 24 is 75%. A zero total cannot be used as a divisor.
Measure percentage change
Choose Percentage change and enter the original and new numbers. A change from 80 to 100 is a 25% increase: (100 − 80) ÷ 80 × 100. The return from 100 to 80 is a 20% decrease, because the starting number is different. For negative starting values this tool divides by the absolute value of the starting number; interpretation may depend on your context.
Frequently asked questions
Why can’t I calculate a change from zero?
A percentage change divides by the original amount. Dividing by zero is undefined, so use the absolute difference instead.
How many decimal places are shown?
Results display up to ten fractional digits, with very small or very large results shown in scientific notation. Calculations use JavaScript numbers, so tiny floating-point rounding differences are possible.