How to Use the Percentage Calculator
This free percentage calculator handles the five most common percentage calculations you will encounter in everyday life, school, and work. Simply type numbers into any of the input fields and the result updates in real time. There is no need to press a button or reload the page.
Five Calculation Modes Explained
The first mode answers "What is X% of Y?" which is useful for calculating tips, discounts, and tax amounts. For example, entering 15 and 80 tells you that 15% of 80 is 12. The second mode reverses the question: given two numbers, it tells you what percentage the first number is of the second. This is helpful for test scores or determining what fraction of a budget has been spent.
The third mode calculates percentage change between two values, commonly used in finance, analytics, and reporting. Enter the original value and the new value to see the percent increase or decrease. The fourth and fifth modes let you apply a percentage increase or decrease to a number. These are perfect for calculating sale prices, salary raises, or investment growth.
Common Percentage Formulas
- X% of Y = (X / 100) * Y
- X is what % of Y = (X / Y) * 100
- % change = ((New - Old) / Old) * 100
- Increase by Y% = X * (1 + Y / 100)
- Decrease by Y% = X * (1 - Y / 100)
Practical Applications
Percentages appear everywhere in daily life. Shoppers use them to calculate discounts and sales tax. Students need them for grade calculations. Business professionals rely on percentage change to measure growth, profit margins, and year-over-year performance. Investors track portfolio returns as percentages. Even cooking recipes sometimes call for adjustments by percentage when scaling servings up or down.
Privacy and Accuracy
All calculations are performed entirely in your browser using JavaScript. No data is sent to any server. Results are computed with full floating-point precision and rounded to a reasonable number of decimal places for display. This tool works offline once the page has loaded and is completely free to use with no sign-up required.