In short: A percentage is a fraction of 100: X% of Y is Y × X ÷ 100, and the percentage change from A to B is (B − A) ÷ |A| × 100.
About Percentage Calculator
Percentages show up everywhere — discounts, tips, exam scores, salary raises, inflation, conversion rates — but the three or four formulas behind them are easy to mix up. Is a rise from 50 to 65 a 30% increase or 23%? (It is 30%; going back down from 65 to 50 is a 23% decrease.)
Each calculator on this page answers one question type and shows the formula used, so you can check the logic or reproduce it in a spreadsheet. Results update as you type.
How to use Percentage Calculator
- Find the line that matches your question.
- Type your numbers into its boxes.
- Read the answer and formula underneath — it updates as you type.
- Use the increase/decrease line for prices with tax, raises or markdowns.
Examples
15% of 80 = 12 (80 × 15 ÷ 100).
Visitors went from 50 to 65: (65 − 50) ÷ 50 × 100 = 30% increase.
Frequently asked questions
How do I calculate a percentage of a number?
Multiply the number by the percentage and divide by 100. 15% of 80 = 80 × 15 / 100 = 12.
What is the formula for percentage change?
(new − old) ÷ |old| × 100. A positive result is an increase, a negative one a decrease.
Why does a 20% increase followed by a 20% decrease not return to the start?
The second percentage applies to a larger base. 100 + 20% = 120, and 120 − 20% = 96.
What is the difference between percent and percentage points?
If a rate goes from 4% to 5%, it rose by 1 percentage point, which is a 25% relative increase.
Updated November 2026 · Free, no signup · How we build and test tools