Free Math & Percentage Calculators

Why use these calculators?

Percentages, fractions and averages come up constantly — in shopping, budgeting, school, work reports and recipes — yet the arithmetic is easy to get subtly wrong. Picking the wrong base for a percentage, adding stacked discounts instead of multiplying them, or averaging numbers that should be weighted are some of the most common mistakes people make with everyday math. Each calculator on this site is built to answer one question well, and to show you how the answer was reached so you can trust it and repeat it on your own.

Every page follows the same layout: the calculator first, then a short explanation of the formula, several worked examples you can check by hand, notes on how to read the result, and a section on the limits of the method — the situations where a simple formula can mislead. Results include a visual element such as a percentage bar, comparison bars, a fraction circle, a number line or a grade gauge, because seeing the size of a number is often the fastest way to spot a typo.

Which calculator do I need?

• You know a percentage and a number and want a part of it — for example a 15% tip — use the Percentage Calculator. It also answers "what percent is this of that" and "this is X% of what".
• You have a before and after value and want to know how much it changed in percentage terms — prices, traffic, test scores — use the Percentage Change Calculator.
• You want to apply a rise such as a pay raise, markup or sales tax to a number, use the Percentage Increase Calculator.
• You want to apply a cut such as a discount or depreciation, use the Percentage Decrease Calculator.
• You are working with fractions in homework, recipes or measurements, the Fraction Calculator adds, subtracts, multiplies and divides and simplifies the answer.
• You have a list of numbers and want the typical value, the Average Calculator gives the mean, median, sum and count.
• You have scores with different weights, the Grade Calculator combines them into a weighted average and letter grade.
• You need to count days or find a date — a deadline, a notice period, someone's exact age — use the Days Between Dates, Age or Add or Subtract Days calculators in the Date & Time section.
• You are switching between metric and imperial, the Unit Converters cover length, weight and temperature with exact factors, including quick cm to inches, kg to lbs and °F to °C pages.
• You have a word or character limit, paste your text into the Word Counter or Character Counter.

Accurate, private and fast

All calculations run locally in your browser using plain JavaScript. Nothing you type is sent to a server or saved, and there is no account to create. Pages are lightweight — a single small stylesheet and script shared across the site — so they load quickly even on a slow mobile connection, and they work on phones, tablets and desktops alike.

Inputs are checked before calculating. If a value is missing, isn't a number, or would cause an impossible operation such as dividing by zero, you get a plain-English message explaining what to fix rather than a confusing "NaN" or "Infinity". Results are shown with sensible rounding and thousands separators, while the underlying math keeps full precision.

Learn the method, not just the answer

Calculators are most useful when they also teach. Each tool shows the formula with your own numbers substituted in, so a student can follow the steps and an adult can double-check a bill or report. The worked examples on each page cover the common cases plus tricky ones — negative numbers, values above 100%, improper fractions and skewed data — so you know what to expect before you rely on a result.