Percentage Calculator

1. Select the type of percentage calculation using the tabs.
2. Enter the required values in the input fields.
3. The result is calculated automatically as you type.

What is a Percentage?

A percentage is a way of expressing a number as a fraction of 100. The word comes from the Latin "per centum," meaning "by the hundred." Percentages are used extensively in everyday life for discounts, taxes, tips, interest rates, statistics, grades, and financial calculations. This tool provides five common percentage operations: finding a percentage of a number, determining what percentage one number is of another, calculating percentage change, finding the original value before a percentage was applied, and adding or subtracting a percentage.

How Percentage Calculations Work

The fundamental formula is: percentage = (part / whole) * 100. To find X% of Y, multiply Y by X/100. To find what percentage X is of Y, divide X by Y and multiply by 100. Percentage change between an old value and a new value is calculated as ((new - old) / old) * 100. A positive result indicates an increase, a negative result indicates a decrease. These formulas cover the vast majority of percentage problems you will encounter in daily life, academics, and professional work.

Common Use Cases

• Calculating sale prices and discounts (e.g., 25% off a $80 item = $60)
• Determining tips at restaurants (e.g., 18% of $45 = $8.10)
• Computing sales tax amounts on purchases
• Analyzing financial metrics like profit margins and ROI
• Converting between fractions, decimals, and percentages
• Calculating grade percentages from test scores

Common Percentage Mistakes

A frequent mistake is assuming that percentage increases and decreases are symmetric. If a stock rises 50% and then falls 50%, it does not return to its original value. Starting at $100, a 50% increase brings it to $150, but a 50% decrease from $150 brings it to $75, not $100. Similarly, a 10% discount followed by a 10% tax does not yield the original price. Understanding this asymmetry is important in finance, statistics, and any field where percentages are applied sequentially.

For financial calculations, try the Discount Calculator or Tip Calculator. For academic grade calculations, see the Grade Calculator.