How We Check Our Maths

Every calculator on this site is built from a published, standard formula — and we show you which one, so you never have to take our word for it.

1. We start from a published formula

We do not invent methods. Each tool implements a formula from a standard reference, and the formula is printed on the calculator page itself. Where a field has more than one accepted convention, we state which one we use and why.

2. We test against worked examples

Before a calculator is published we run it against examples whose answers are already known, including the awkward cases: zero, negative values, very large numbers, and rounding boundaries. A tool that disagrees with a known answer does not ship.

3. We show the working

Wherever it is useful, the result is accompanied by the steps that produced it. If you can follow the steps, you can check us.

4. We re-check when we change something

Any change to a calculation is re-tested against the same examples before it goes live.

5. We fix errors quickly and say so

If you find a wrong answer, please report it. We investigate, correct it, and note significant corrections on the affected page.

What this is not

Our tools are for general information and education. They are not financial, medical, legal, tax or engineering advice. For decisions that matter, check with a qualified professional.