Percentage calculator
A percentage is a way of writing a fraction out of 100. The same idea answers three different questions: what is X percent of Y, what percent is X of Y, and how much did a value rise or fall.
This page keeps the three questions separate so the labels match the numbers you type. The formulas are short enough to check on paper.
Calculator
Required fields are marked with *.
Use a comma or a dot for the decimal, as in 12.5 or 12,5. Type thousands as 1000 or 1 000. A single comma or dot is the decimal mark, so 1,000 means 1.
Results
The result will appear here.
How to use this calculator
- Choose the question you actually have.
- Enter the numbers. A comma or a dot can mark the decimal.
- Press Calculate and compare the sentence with the formula below.
Formula
“X percent of Y” multiplies the base by the percent divided by 100.
result = (percent / 100) × base
“X is what percent of Y” divides the part by the whole and multiplies by 100. The whole cannot be zero.
result = (part / whole) × 100
Percent change uses the size of the starting value as the denominator, so a positive result means the new value is higher even if the start was negative. Change from zero is undefined.
result = (new − old) / |old| × 100
Worked example
15 percent of 80
15 divided by 100 is 0.15. Multiply 0.15 by 80 and the result is 12.
The other two questions use the same page: 20 is 25 percent of 80, and a move from 40 to 50 is a 25 percent increase.
15% of 80 is 12.
Questions
Why is 1,000 read as 1?
A single comma or dot is the decimal mark, so 1,000 means one and three decimal places. Type 1000 or 1 000 for one thousand.
Can the starting value of a percent change be negative?
Yes. The denominator is the absolute value of the start, so the sign of the result follows the direction: positive means the new number is higher.
Is this a tax calculator?
No. It is ordinary percentage arithmetic. Tax rules depend on the place and on what is being taxed.
Sources
Last reviewed November 1, 2026