Methodology

The site is built to stay accurate as the catalogue grows from a few dozen calculators to several thousand. The rule: a deterministic engine, unique content, real sources.

Calculations without AI

Every result comes from a tested TypeScript function. AI may help draft an explanation; it never produces the number. The same inputs always give the same result.

Choosing formulas

We do not invent formulas. Math: standard identities. Finance: classic amortization and compound interest at a nominal rate, with no implied APR. Health: cited publications (Mifflin-St Jeor 1990, WHO for BMI, EFSA for protein and water, Hodgdon & Beckett 1984 for circumferences). Jobsite: geometry plus a waste allowance, with typical densities clearly labelled as such.

Health and finance

No manufactured medical or financial expertise, and no “reviewed by a doctor” until a real reviewer exists. Sensitive pages carry a warning. Unsourced statistics are refused.

Rounding

Internal math uses JavaScript IEEE-754 floating point. The display rounds for reading (often 0 to 4 decimals, currency to 2). A bank or a spreadsheet may differ by a cent.

Updates

Every calculator carries a lastUpdated field. A formula change requires a unit test and a visible date. Pages that are not ready stay out of the sitemap (published: false).

Languages

The site is published in six languages: French, English, Spanish, Portuguese, German and Arabic. Each language has its own URL prefix, translated slugs, its own titles and descriptions, and hreflang tags. French remains the reference version (x-default). The calculation engines are shared: only the content layer changes.

Sources

A source has an id, a title, a publisher and a URL. It is stored once and reused. No phantom citation, no invented DOI. The public list is on the sources page.