Percentage Calculator
TOOLThree calculators in one: a percent of a number, one number as a percent of another, and the percent change between two numbers.
A percentage is just a number expressed as a fraction of 100 — the word literally means "per hundred." This calculator covers the three questions people ask most often, and each one updates the moment you change a value.
The three formulas
What is X% of Y? Divide the percentage by 100 and multiply by the number: result = (X ÷ 100) × Y. So 25% of 80 is (25 ÷ 100) × 80 = 20.
X is what percent of Y? Divide the part by the whole and multiply by 100: percent = (X ÷ Y) × 100. So 15 out of 50 is (15 ÷ 50) × 100 = 30%.
Percentage change from A to B? Take the difference, divide by the starting value, and multiply by 100: change = ((B − A) ÷ A) × 100. Going from 40 to 50 is ((50 − 40) ÷ 40) × 100 = +25%. A negative answer means the value went down.
"Percent of" and "is what percent of" are inverses. If 15 is 30% of 50, then 30% of 50 should give you back 15. Swapping between the tabs above is an easy way to verify your own arithmetic.
A worked example
Suppose a total of 200 units is split so that one group accounts for 50 of them. To express that group as a share, use the second mode: (50 ÷ 200) × 100 = 25%. If that group later grows to 70 units, the percentage change in the group's size is ((70 − 50) ÷ 50) × 100 = +40%. Notice that a 40% rise in the group does not mean it now holds 40% of the total — share and change are different questions, which is exactly why the calculator keeps them on separate tabs.
From percentages to charts
Percentages are the natural input for any chart that shows composition. Once you know each category's share of a whole, those shares become the slices of a pie chart, where the full circle is 100% and each slice's angle is proportional to its percentage. A 25% category fills a quarter of the circle; a 50% category fills half. If you would rather compare percentages side by side instead of as slices, a bar chart plots each share as a labelled bar.
When your numbers are ready, the pie chart maker turns a list of values into a finished pie or donut you can export, and make a chart lets you pick whichever chart type fits the story your percentages tell.