A percentage calculator is an essential math tool that helps you quickly solve the three most common percentage problems: finding a percentage of a number, determining what percent one number is of another, and calculating the percentage change between two values. Whether you are figuring out a discount, analyzing data, or checking a markup, this tool gives you instant answers with no manual math required.
What is X% of Y?
X is what % of Y?
Percentage Change from X to Y
Increase or Decrease a Number by X%
How to Use the Percentage Calculator
Percentages appear everywhere in daily life: sales tax, discounts, tips, grades, interest rates, data analysis, and more. Our percentage calculator gives you four easy-to-use tools in one page, each designed for a specific type of percentage problem. All calculations happen instantly as you type, so there is no need to click a button or wait for results.
Find X% of a Number
The first calculator answers the most common percentage question: "What is X% of Y?" Enter the percentage in the first field and the base number in the second field. For example, to find 15% of 200, enter 15 and 200 to get 30. Use the quick-select buttons (5%, 10%, 15%, 20%, 25%, 50%, 75%) to instantly set commonly used percentages. The swap button reverses the two inputs, making it easy to try different scenarios.
Find What Percent X Is of Y
The second calculator determines the percentage relationship between two numbers. Enter the part in the first field and the whole in the second. For example, if you scored 42 out of 50 on a test, enter 42 and 50 to see that you scored 84%. This is useful for calculating grade percentages, completion rates, market share, and similar proportion-based metrics.
Calculate Percentage Change
The third calculator shows the percentage increase or decrease between an original value and a new value. Enter the starting number and the ending number to see the change expressed as a percentage. For instance, if a stock price went from $200 to $250, the result shows +25%. If it dropped from $250 to $200, it shows -20%. The result is color-coded: green for increases and red for decreases. This is essential for tracking price changes, investment returns, sales growth, and performance metrics over time.
Increase or Decrease by a Percentage
The fourth calculator applies a percentage increase or decrease to any number. Enter a value, choose whether to increase or decrease, and enter the percentage. For example, increasing 200 by 25% gives 250, while decreasing 200 by 25% gives 150. This is perfect for calculating sale prices, markups, tax-inclusive amounts, and projected growth. Quick-select buttons let you apply common percentages with a single click.
Frequently Asked Questions
Is this percentage calculator free to use?
Yes, this percentage calculator is completely free with no ads, no signup, and no limits. All calculations run locally in your browser, so you can use it anytime — even offline after the page loads.
Is my data private when I use this tool?
Absolutely. Everything runs entirely in your web browser using client-side JavaScript. No numbers or calculations are ever sent to a server. Your data stays on your device at all times.
How do I calculate what percent one number is of another?
Use the second calculator card: enter the part (X) and the whole (Y), and the tool instantly shows what percentage X is of Y. The formula is (X / Y) x 100. For example, 30 is 15% of 200 because (30 / 200) x 100 = 15%.
How do I calculate percentage change between two numbers?
Use the third calculator card: enter the original value and the new value. The tool calculates the percentage increase or decrease using the formula ((New - Old) / Old) x 100. A positive result means an increase; a negative result means a decrease.
What is the formula for finding X% of a number?
To find X% of a number Y, multiply Y by X and divide by 100. For example, 15% of 200 is (200 x 15) / 100 = 30. The first calculator card does this for you automatically as you type.
Can I use this for percentage increase and decrease?
Yes, the percentage change calculator handles both increases and decreases. Enter the original value and the new value, and it will show a positive percentage for increases and a negative percentage for decreases. The result is color-coded green for increases and red for decreases.
What are the quick percentage buttons for?
The quick buttons (5%, 10%, 15%, 20%, 25%, 50%, 75%) let you instantly set common percentage values without typing. Click any button to fill the percentage field and see the result update in real time. These cover the most commonly used percentages for tips, discounts, and markups.