Editorial policy

Sources

Formulas, rates and thresholds come from primary sources: published legislation, standards bodies, official statistics and regulators. Where a figure comes from the law — tax slabs, for instance — it is read from the legislation itself rather than from a news report or another calculator, and the page links to it.

We do not use another calculator site as a source for anything.

Testing

Before a calculator is published:

• Its expected results are established independently of our own code — worked out by hand, taken from a published table, or computed by a separate method.
• Those results become automated tests that run on every change, so a future edit cannot silently break a formula that was once right.
• Where the same quantity can be derived two ways, both are implemented and checked against each other. Where a public reference exists, results are compared against it.
• Edge cases are tested deliberately: zero, negative values, very large numbers, invalid text, and the boundaries between bands or brackets.

Review dates

Every calculator shows when its formula and sources were last checked. Anything that depends on a rate, a threshold or a tax year also shows which year it applies to, near the top of the page, so nobody has to guess whether they are looking at current figures.

Pages tied to annual changes — tax, in particular — are reviewed when the relevant law changes.

Corrections

If something is wrong, it gets fixed and the review date is updated. Where an error could have materially misled someone, the page will say what changed rather than quietly editing it.

Report anything that looks wrong through the contact page.

Advertising and independence

This site is funded by advertising, and may in future carry affiliate links on some finance pages. The rules:

• Advertisers have no influence over any calculation, article, ranking or recommendation.
• Advertising is visually distinct from content and never disguised as editorial.
• Any link that earns a commission is disclosed on the page that carries it.
• No page recommends a product in exchange for payment.

Written content

Everything here is written for this site. Explanations, examples, tables and FAQs are original work, not copied or reworded from other calculator sites. Facts are attributed where they come from someone else.

Content is written to be understood by someone with no background in the subject, without talking down to anyone, and without padding a page to make it longer than the explanation needs to be.

Limits we state openly

Every calculator says what it does not include. A mortgage calculator that ignores insurance and closing costs is useful; one that pretends those do not exist is misleading. Where a result is an estimate, the page says so and explains what would change it.

Finance, health and tax pages carry a standing note that they are information rather than professional advice.