Online calculators

These calculators cover the small calculations that come up all the time: how much is 15% of a bill, how old someone is today, or how many days remain until a deadline. Each one shows the result straight away and explains the formula behind it, so you can check the logic instead of trusting a black box.

Everything is calculated on your device. Nothing you type is sent anywhere, and no account is needed.

Tools in this category

Age CalculatorExact age in years, months and days, from any date of birth.Date CalculatorNewDays between two dates, or add and subtract time from a date.Percentage CalculatorFive common percentage calculations, answered as you type.

Common questions

Are the results exact?

Yes. The calculators use exact calendar arithmetic and standard floating-point maths, and display results rounded only for readability. Each tool page explains its formula so you can verify it by hand.

Do you store what I enter?

No. Calculations run in your browser and the values you type never leave your device.