Free calculator
Percentage calculator
The three most common percentage calculations: how much is X % of a number, what percentage one number is of another, and by what percentage a value changed. The result updates as you type.
How much is X % of a number
For example: how much is 15 % of 800?
- Result
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What percentage is a number of a number
For example: what percentage is 120 of 800?
- Result
- — %
Percentage change
By what percentage did the value rise, or fall? A negative result means a drop.
- Change
- — %
How percentages are calculated
The word "percent" comes from the Latin per centum, meaning "per hundred". When we say "50 percent", we mean 50 out of every hundred, that is, a half.
How much is X % of a number?
You multiply the base by the percentage expressed as hundredths:
X % of Y = Y × (X / 100)
For example, 20 % of 500: 500 × (20 / 100) = 100. So 20 % of 500 is 100.
What percentage is number X of number Y?
You multiply the ratio of the two numbers by one hundred:
(X / Y) × 100
For example, what percentage is 300 of 1,500: (300 / 1500) × 100 = 20 %.
By what percentage did a value change?
You divide the difference between the new and original value by the original value:
((new − original) / original) × 100
For example, from 800 to 920: ((920 − 800) / 800) × 100 = +15 %. When a value falls, the result is negative: from 800 to 600 the change is −25 %.
Mind the direction: "by what percent is A bigger than B" and "by what percent is B smaller than A" are not the same numbers. 200 is 33.3 % more than 150, but 150 is 25 % less than 200. You always divide by the value the change is measured from.
Where percentages are used most often
- Finance: interest rates, investment returns, inflation.
- Retail: a "−30 %" sale means a price reduced by 30 percent; margin and markup are also just percentages (and often get confused).
- Statistics: probabilities, survey results, market shares.
- School: test scores as a percentage of the maximum points.
Where to go next
You can do the maths. But what next? How to turn customers who bought once into customers who buy repeatedly is the subject of the book Opakovaný prodej.