Percentage Calculator
Find a percentage of a number, what percent one number is of another, or percent change.
Inputs
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Formula
X% of Y = (X ÷ 100) × Y
The same calculator also inverts this to find what percent X is of Y, and computes the percent change between two numbers.
Worked example
20% of 500 is 100 — the classic sanity-check example, useful for confirming the calculator matches mental math before trusting it on harder numbers.
Where this can give the wrong answer
- "X is what percent of Y" is undefined when Y is 0 — the calculator reports this as an error rather than showing Infinity.
- Percent change from a starting value of 0 is undefined for the same reason: any change from zero is an infinite percentage increase.
- A percent change can exceed 100% (e.g. going from 10 to 50 is a 400% increase) — this is correct, not a bug, and trips people up more often than the arithmetic itself.
FAQ
- If a rate moves from 10% to 12%, that's a 2 percentage point increase but a 20% relative increase — this calculator's 'percent change' mode gives you the relative figure. Confusing the two is one of the most common statistics-reporting errors in the news.