Percentage Calculator
Three ways to calculate percentages. Find what X% of a number is, what percentage one number is of another, or the percentage change between two values.
How to Calculate Percentages
A percentage expresses a number as a fraction of 100. The word "percent" comes from the Latin "per centum" meaning "by the hundred." Percentages are used everywhere — from calculating discounts and tips to tracking investment returns and test scores.
The three percentage formulas
| Question | Formula | Example |
|---|---|---|
| What is X% of Y? | Result = Y × (X ÷ 100) | 20% of 150 = 150 × 0.20 = 30 |
| X is what % of Y? | Result = (X ÷ Y) × 100 | 30 is what % of 200? = (30÷200)×100 = 15% |
| % change from X to Y | Result = ((Y - X) ÷ X) × 100 | 80 to 100 = ((100-80)÷80)×100 = 25% increase |
Frequently Asked Questions
How do I find 15% of a number quickly?
To find 15% of any number, find 10% first (move the decimal point one place left), then add half of that (5%). For example: 15% of 200 = 10% (20) + 5% (10) = 30. This mental math trick is especially useful for calculating tips at restaurants.
What is the difference between percentage and percentage points?
These are two different things that are commonly confused. A percentage is a ratio relative to a base. A percentage point is an absolute difference between two percentages. For example, if interest rates rise from 2% to 3%, that is an increase of 1 percentage point, but a 50% increase relative to the original rate. When comparing percentages, always clarify which you mean.
How do I calculate a percentage decrease?
Use the percentage change formula: ((New Value - Old Value) ÷ Old Value) × 100. If the result is negative, it is a percentage decrease. For example, a price drops from $50 to $35: ((35 - 50) ÷ 50) × 100 = -30%. This represents a 30% decrease in price.