How we source, check and maintain the numbers

Official sources, named on the page

Every tax rate, threshold, allowance and benefit figure comes from a primary, official publication: the revenue or statistics authority that actually sets the number. For the United Kingdom that means HMRC; for the United States the IRS and the relevant state revenue department; for other markets the national tax authority. We do not take figures from aggregator sites or copy tables from other publishers. The source for each calculator is listed on its own page, with a link, so you can check it yourself.

Tested against known results before publishing

A calculator is only as good as the result it returns. Each country tax engine ships with a set of reference cases: worked examples whose correct answer is already known from the official guidance. The engine has to reproduce every one of those answers before it is allowed to go live. If a calculator does not match the official worked example, it does not publish. Headline figures are also cross-checked a second time against an independent official source, so a single transcription mistake cannot slip through.

Dated, and reviewed when the rules change

Tax rules change every year, and a figure with no date is a figure you cannot trust. Each calculator shows the tax year it applies to and when it was last reviewed. When a budget or rate change lands, the affected calculators are re-derived from the new official figures and re-tested against fresh worked examples, not nudged by hand. The economic datasets behind the comparison tools are refreshed on a schedule from their original publishers.

Every page is written, not generated by template

We do not spin one article into fifty near-identical copies. Each page is written for its specific country and calculator, with its own real numbers, examples and explanations. Before anything is published it is checked for duplicated phrasing against the rest of the site, and pages that would only differ by a swapped word or number are not built at all. The aim is one genuinely useful page rather than many thin ones.

Health and medical figures

The health calculators (such as BMI, calorie needs, body fat and pregnancy dating) use established, published formulas and reference ranges, for example the Mifflin-St Jeor equation for energy needs and guidance from bodies such as the NHS and ACOG. These tools give general estimates for information only. They are not a diagnosis and not a substitute for advice from a qualified health professional.

The comparison and data tools

The purchasing power, cost of living and quality of life tools are built on openly published, reusable datasets: World Bank World Development Indicators, US Bureau of Economic Analysis Regional Price Parities, United Nations Human Development Report indicators, and Eurostat. Each dataset is used under its own licence, credited on the tool, and baked into the site so the figures are stable and traceable rather than pulled live from a third party.

What these tools are, and are not

Everything here is an estimate for general guidance. The figures depend on assumptions that may not match your exact situation, and rules and prices change. Nothing on this site is financial, tax, legal or medical advice. Always confirm with the official sources, or a qualified professional, before making a decision that matters.

Corrections

If you find a figure that looks wrong, please tell us. We take corrections seriously, check them against the official source, and fix confirmed errors quickly. National Calculators is an independent project, built and maintained by Vikas Dulgunde, and is not affiliated with any government or tax authority.