About

This site gathers the calculators people reach for most often in one clean place, together with plain-language guides that explain the maths behind them. The aim is simple: give you a correct answer quickly, and help you understand it well enough to check it yourself. There is nothing to install, no account to create and nothing to pay.

The seven calculators

• Basic calculator. Everyday arithmetic with the usual order of operations, a percent key, and a preview of the answer as you type. Your last five calculations are kept on your device so you can reuse them.
• Scientific calculator. Powers, roots, logarithms, factorials, trigonometry in degrees or radians, and E notation for very large or very small numbers.
• Percentage calculator. The common percentage questions in one place: a percent of a number, what percent one number is of another, percent change, and adding or taking off a percentage.
• Date calculator. Days between two dates (with and without counting both ends), a date a number of days from another, and countdowns.
• Time calculator. The difference between two clock times, including across midnight, and a time plus hours and minutes.
• Age calculator. Age in completed years and in years, months and days, with February 29 birthdays handled.
• Fraction calculator. Adding, subtracting, multiplying and dividing fractions and mixed numbers, with the result simplified and shown as a decimal too.

How the results are checked

• The calculation engine has automated tests that compare its results with hand-checked answers, including edge cases such as leap years, February 29 birthdays, division by zero, negative numbers and very large values. The tests are run again after changes to the code.
• Before launch, the calculators were tried by eight people of different ages and backgrounds, from an elementary-school student to someone in their seventies. Problems they ran into, from confusing messages to keys that behaved unexpectedly, were fixed.
• The text on every page was reviewed twice by native speakers, so the explanations read naturally rather than like a machine translation.
• Results are rounded to 12 significant digits to avoid the small binary rounding errors that computers make with decimals, so 0.1 + 0.2 shows 0.3.
• Dates are counted as whole calendar days, so time zones and daylight saving time do not change the result.

Even so, mistakes are possible. Results are for general reference only. For legal, medical or financial decisions, please confirm with an official source or a professional.

Guides

The guide section explains the ideas behind each calculator with worked examples you can check by hand: percentages and discounts, percent change, ratios, averages, rounding, the order of operations, counting days and leap years, ages, time and decimal hours, fractions and decimals, and logarithms. Each guide links to the calculator that does the same job, so you can learn the method and then try your own numbers.

Privacy

Everything is calculated in your browser: what you type is not sent to or stored on our servers, and the details are in the privacy policy.

Languages

The site is available in several languages, and each version was reviewed by native speakers. Use the language menu at the top of any page to switch.

Contact

The site is run by an independent site operator. If you find a wrong result, a confusing explanation or a typo, or you have a suggestion, please get in touch. Reports of errors are especially welcome and are checked and corrected as quickly as possible. Email [email protected].