Percentage Calculator
Three common percentage questions, one tool.
How to use this calculator
Pick which kind of percentage question you have from the menu — a percent of a number, what percent one value is of another, or the change between two values — then fill in the two boxes and press Calculate. The labels change to match the mode so it is always clear what to enter. The result appears with a short line of working so you can see how it was reached. It covers the everyday cases: discounts, tips, tax, test scores, and tracking how much something went up or down.
The formulas explained
Each mode uses one simple rule:
percent of: (X ÷ 100) × Y · is what %: (X ÷ Y) × 100 · change: ((Y − X) ÷ X) × 100
A percentage is just a fraction out of 100, so "per cent" literally means "per hundred". To take a percent of a number you convert the percent to a decimal and multiply. To find what percent one number is of another you divide and scale up by 100. Percentage change compares the difference between two values to the starting value, which is why a rise from 50 to 75 is a 50% increase rather than 25%.
A worked example
To find 25% of 80, convert 25% to 0.25 and multiply: 0.25 × 80 = 20. To check what percent 20 is of 80, divide: 20 ÷ 80 = 0.25, or 25%. And the change from 80 down to 20 is (20 − 80) ÷ 80 × 100 = −75%, a 75% decrease. The calculator handles each of these from the matching mode.
Frequently asked questions
How do you find a percentage of a number?
Divide the percent by 100 and multiply by the number — 25% of 80 is 0.25 × 80 = 20.
How do you calculate percentage change?
Subtract the old value from the new, divide by the old value, and multiply by 100.
What percent is X of Y?
Divide X by Y and multiply by 100.