calculatorproCalculators that show their working

All 10 calculators

The complete list, grouped by what you are trying to work out. Each one shows the arithmetic behind its answer and says plainly what it hasn't counted — and each has a guide explaining the maths, if you want the reasoning as well as the number.

Free, no limits
No account needed
Nothing leaves your browser

Everyday maths

Percentage CalculatorPercentage of a number, increase, decrease and difference.Guide →
Age CalculatorExact age in years, months and days — or the gap between any two dates.Guide →
Ratio CalculatorSimplify a ratio, scale it up, or find the missing part.Guide →
Hours CalculatorAdd up worked hours between two times, across days or a whole week.Guide →

Converting

Unit ConverterLength, weight, volume and temperature — cm to feet, kg to pounds and back.Guide →

Money

Compound Interest CalculatorWhat savings grow to, year by year, with the working shown.Guide →

VAT & tax

VAT CalculatorAdd or remove VAT at 20%, 5% or a rate you set.Guide →

Selling online

Health

BMI CalculatorBody mass index from height and weight, in metric or imperial.Guide →

Prefer to read how it works?

There are 10 guides — one per calculator — explaining the formula in plain English, with worked examples and an honest note on where each method stops being reliable.

Read the guides