The method

Where the numbers come from

Every rule that goes into a calculator (tax rates, thresholds, limits, conversion factors) comes from an official source: government agencies such as the IRS, the CFPB or GOV.UK, public bodies, and the law itself.

At the bottom of every page you’ll find the sources, with links, and the date they were last checked.

How a formula is tested

Every formula is tested against examples with a known answer, worked out by hand, and against official worked examples when they exist. If a test fails, the page doesn’t go live.

Each page shows the worked example step by step, so you can redo it with a calculator.

When the rules change

Numbers that change every year are kept in one place. When a new rule comes out, they’re updated there, and every page that uses them updates at the same time.

What it isn’t

A calculation here is a careful estimate, not advice: it can’t account for your whole situation. Before you decide, check with a professional. The legal information page goes into more detail.

Who makes it, and with what tools

This site belongs to me, Ciro Simone Irmici. I write it and build it. I also use artificial intelligence tools for the code and the writing, but every number and every rule is checked against official sources before it goes live.

There are no sponsors and no recommended products on the pages. Where one of my own apps fits the topic, you’ll find it at the bottom, under its own name. It’s mine, and I say so.

Your numbers stay yours

The calculations run in your browser, so the numbers you type aren’t sent to any server. The details are on the privacy page.

Spotted a mistake?

Write to me at [email protected]. I’ll check it, fix it and update the date on the page.