Understanding Percentages
A percentage expresses a number as a fraction of 100. Percentages show up everywhere — discounts, taxes, exam scores, interest rates, tips, and statistics — so being able to work with them quickly is a genuinely useful everyday skill. This page bundles the three most common percentage questions into one tool so you never have to remember which formula to use.
How Each Mode Works
"X% of Y" multiplies Y by X/100, answering questions like "what is 20% of 150?" (answer: 30). "X is what % of Y" divides X by Y and multiplies by 100, answering questions like "30 out of 150 is what percent?" (answer: 20%). "Percentage increase/decrease" compares two numbers and reports how much the value changed relative to the starting point, using the formula (Y − X) / X × 100 — useful for tracking price changes, salary raises, or growth rates.
FAQ
Can percentages be negative?
Yes. In the increase/decrease calculator, a negative result means the value decreased — for example going from 100 to 80 is a −20% change.
What's the difference between percentage change and percentage points?
Percentage change is relative (e.g. a rate going from 10% to 15% is a 50% relative increase), while percentage points is the raw difference (5 points). This calculator computes relative percentage change.
How do I calculate a percentage by hand?
Divide the part by the whole, then multiply by 100. For example, 45 out of 60 is (45/60) × 100 = 75%.