About this site

NumberOneCalc collects the calculations people look up most often — loan instalments, tax on an invoice, body mass index, the gap between two dates, unit conversions — and puts them in one place with a consistent layout.

How the calculations run

Every calculator runs in your browser using plain JavaScript. Nothing you type is sent to a server, which is why results appear instantly and why we have nothing to store. The only thing recorded is an anonymous count of how many times each calculator page is used, so we know which ones to improve.

Why every page shows its formula

A number with no working behind it is hard to trust. Each page states the formula it uses, walks through one worked example and breaks the result into its parts, so you can check the answer against your own arithmetic or your bank's statement.

What these results are not

They are estimates, and they are only as good as the assumptions you enter. Lenders round differently, tax rules change, and health formulas describe populations rather than individuals. For anything that carries real consequences — a loan you are signing, a tax filing, a medical decision — check the figure with a qualified professional.

Found something wrong?

If a result looks off, the fastest fix is a message describing what you entered and what you expected. Corrections are welcome — several formulas here have been sharpened that way.