Percentage Calculator
A percentage calculator solves the three most common percent problems instantly: finding X% of a value (what is 15% of 200?), determining what percent one number is of another (30 is what percent of 120?), and computing the percentage change between two values (from 80 to 100 is a 25% increase). Percentages express a part per hundred, which is why they are the universal language of discounts, interest rates, taxes, statistics, and grades.
Doing these conversions mentally is error-prone, especially with percentage change, where people often divide by the wrong base. This tool applies the correct formula for each mode and shows the result immediately. A useful property to remember: X% of Y always equals Y% of X, so 8% of 50 is the same as 50% of 8, which is 4. That trick, combined with this calculator, makes everyday percent math fast and reliable.
How it works
Each mode uses a specific formula. X% of Y = (X ÷ 100) × Y. To find what percent X is of Y: (X ÷ Y) × 100. Percentage change from an old value to a new value: ((new − old) ÷ old) × 100 — the denominator is always the original value, which is why a 50% increase followed by a 50% decrease does not return to the starting number (100 → 150 → 75).
Use cases
- Calculating a discount: how much you save with 25% off a $80 item
- Finding a test score as a percentage: 42 correct answers out of 60 questions
- Measuring price or salary change: the percent increase from last year to this year
- Computing sales tax, tips, or commission on top of a base amount
Frequently asked questions
How do I calculate the percentage of a number?
Divide the percentage by 100 and multiply by the number: X% of Y = (X ÷ 100) × Y. For example, 15% of 200 = 0.15 × 200 = 30. A quick shortcut is to find 10% first (move the decimal one place) and scale from there.
How do I calculate percentage change between two numbers?
Subtract the old value from the new value, divide by the old value, and multiply by 100: ((new − old) ÷ old) × 100. Going from 80 to 100 is ((100 − 80) ÷ 80) × 100 = 25% increase. A negative result means a decrease.
What is the difference between percentage points and percent?
Percentage points measure the absolute difference between two percentages, while percent measures relative change. If a rate rises from 10% to 12%, that is an increase of 2 percentage points, but a 20% relative increase, because 2 is 20% of the original 10.
How do I find what percent one number is of another?
Divide the part by the whole and multiply by 100: (X ÷ Y) × 100. For example, 30 out of 120 is (30 ÷ 120) × 100 = 25%. This is the formula used for test scores, market share, and completion rates.
Why doesn't a 50% increase then a 50% decrease cancel out?
Because each percentage is applied to a different base. Starting at 100, a 50% increase gives 150; a 50% decrease is then taken from 150, removing 75 and leaving 75, not 100. To undo a 50% increase you would need a 33.33% decrease.