Percentage Calculator
By Shaheer Bin Ramzan
Reviewed November 2026 · Formula sources
Pick the question you are asking, enter two numbers, and get the answer with the working written out.
Percentage formulas
A percentage is a number expressed as a fraction of 100. The word comes from the Latin per centum, meaning "by the hundred". Three formulas cover almost every everyday case.
| Question | Formula |
|---|---|
| X% of Y | X ÷ 100 × Y |
| X is what % of Y | X ÷ Y × 100 |
| Percent change | (new − old) ÷ |old| × 100 |
Worked examples
A discount on a price
A jacket costs 60 and is 25% off. The saving is 25 ÷ 100 × 60 = 15, so the sale price is 60 − 15 = 45.
A test score
You scored 42 out of 56. 42 ÷ 56 = 0.75, and 0.75 × 100 = 75%.
A change in price
Rent rises from 800 to 880. The change is 880 − 800 = 80, and 80 ÷ 800 = 0.10, which is a 10% increase.
Common mistakes
Using the new value as the base for percent change gives the wrong answer; the base is always the starting value. Percentage points also differ from percent: a rate moving from 4% to 6% is up 2 percentage points, but up 50% in relative terms. Finally, adding successive percentages does not work, because each one applies to a different base.
Frequently asked questions
How do you calculate a percentage of a number?
Divide the percentage by 100, then multiply by the number. For example, 15% of 80 is 0.15 × 80 = 12.
How do you find what percent one number is of another?
Divide the part by the whole and multiply by 100. If 18 out of 24 questions are correct, 18 ÷ 24 × 100 = 75%.
How do you calculate percent change?
Subtract the old value from the new value, divide by the old value, then multiply by 100. A positive result is an increase and a negative result is a decrease.
Why is a 50% increase not undone by a 50% decrease?
The second percentage applies to a larger number. 100 up 50% is 150, and 150 down 50% is 75, not 100.
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