Percentage Calculator
Three percentage calculations in one tool: find what X% of a number is, determine what percentage one number is of another, or calculate the percentage change between two values.
How Percentages Work
A percentage is a number expressed as a fraction of 100. The word comes from the Latin per centum, meaning "by the hundred." When you say 25%, you mean 25 parts out of 100 — or the decimal 0.25. Converting between percentages and decimals is simple: divide by 100 to get the decimal, multiply by 100 to get the percentage.
Key Formulas
X% of Y: result = (X / 100) × Y X is what % of Y: result = (X / Y) × 100 % change X → Y: result = ((Y - X) / X) × 100 Quick mental math: 10% of any number: move decimal point one place left 1% of any number: move decimal point two places left 15% tip: take 10% + half of that (5%)
Frequently Asked Questions
How do I calculate 20% of a number?
Multiply the number by 0.20 (or 20 ÷ 100). Example: 20% of 150 = 150 × 0.20 = 30. A mental shortcut: 20% = 10% × 2. Find 10% by moving the decimal point left once, then double it.
What is the difference between percentage and percentage points?
Percentage expresses a part of a whole (e.g., 30% approval rating). Percentage points measure the arithmetic difference between two percentages. If approval rises from 30% to 35%, it rose 5 percentage points — but that is a 16.7% increase in the approval rating itself. Mixing these up is a common error in journalism and statistics.
How do I calculate a percentage increase or decrease?
Percentage change = ((New − Original) ÷ Original) × 100. If a price goes from $40 to $50: ((50 − 40) ÷ 40) × 100 = 25% increase. If it drops from $50 to $40: ((40 − 50) ÷ 50) × 100 = −20% decrease.
What is 100 percent of something?
100% of any number equals that number itself. 100% represents the whole — all of it. 200% means twice the original; 50% means half. Percentages above 100% represent amounts greater than the original whole.