Percentage Calculator
Percentage Calculator
Calculate percentages, increases, decreases, and differences.
Runs entirely in your browser
How to use this tool
- Fill in the inputs.
- Read the result.
- Copy or download as needed.
About the Percentage Calculator
Percentages are one of the most common ways to express a relationship between two numbers, and this Percentage Calculator handles the four situations people run into most often: finding what one number is as a percentage of another, calculating a percentage increase, calculating a percentage decrease, and finding the percentage difference between two values. Instead of memorizing four separate formulas, you simply pick a tab and enter your numbers.
Percentages show up everywhere, from sales tax and tips to exam scores, salary raises, discounts, and year-over-year business growth. Because the underlying math is easy to get backwards under time pressure, a dedicated calculator removes the guesswork and gives you an instant, reliable answer every time you need one.
The "percentage of a number" mode multiplies the percentage by the number and divides by 100, which is the standard definition of percentage (per hundred). The increase and decrease modes both compare the difference between two values against the original (starting) value, then express that ratio as a percentage; this is why the starting value cannot be zero, since dividing by zero is undefined. The percentage difference mode is slightly different: instead of treating one number as the "original", it compares the absolute difference between the two numbers against their average, which is the standard way statisticians express how far apart two values are when neither one is clearly the baseline.
All calculations update instantly as you type, and results include a one-click copy button so you can paste the figure straight into an email, spreadsheet, or report without retyping it.
Common use cases
- Retail and shopping: quickly work out how much a percentage discount actually saves in real currency before you get to the checkout.
- Finance and payroll: calculate a salary increase, a bonus percentage, or how a price has grown or shrunk since last year.
- Education: convert a raw test score into a percentage, or check how much a grade improved between two attempts.
- Business reporting: compare two time periods (last month vs. this month, last quarter vs. this quarter) and express the change as a clean percentage figure for a report or presentation.
- Everyday budgeting: figure out what portion of your monthly income a bill or subscription represents.
Tips and best practices
- Percentage increase and percentage decrease are not symmetrical: a 50% increase followed by a 50% decrease does not bring you back to the original number.
- When comparing two numbers where it is not clear which one is the "before" value, use the percentage difference mode rather than increase or decrease.
- Round only at the very end of a calculation chain — rounding intermediate percentages can introduce small but noticeable errors in the final figure.
- For repeated calculations (like a list of prices), keep this page open in a separate tab so you can flip between entries without losing your place.
