This page describes how everything on this site is made. It is linked from every author box because a claim about accuracy is worth nothing without the method behind it.
Where formulas come from
Every calculator cites the source of its formula, and that source is fetched and read before it is cited — never recalled and never inferred from a summary. The sources are listed at the bottom of each calculator page, linked, so you can check them yourself.
We prefer, in order:
- The body that defines the thing — a government agency, a standards organisation, or the paper that introduced the equation.
- A peer-reviewed paper that prints the equation, clearly labelled as a secondary source, when the primary cannot be retrieved.
- Nothing. If neither is available, the calculator does not ship.
That third option is used. Several calculators sit unbuilt because the authority publishing the formula blocks automated access to its own document, and a health equation reconstructed from memory is exactly the kind of thing that looks authoritative and is wrong.
Where a source is ambiguous
Sources sometimes disagree, or print an equation in a way that can be read two ways. When that happens we say so on the page rather than picking one silently. Two live examples: the blood pressure categories, where two government sources differ on a single word in the definition of a hypertensive crisis — we take the reading that sends someone to a doctor rather than away from one; and the body fat equations, where one paper’s wording would have produced a wrong formula with entirely correct-looking constants, caught only by reading a second paper.
Testing
Every calculator ships with test cases that run automatically before any change is published. A calculator with no test cases fails the build; it is not a warning. Where a published source includes a worked example, that example is used as a test — so the calculator is checked against the authority’s own arithmetic, not only against ours.
Tests cover the edge cases that produce quietly wrong answers: month lengths, daylight saving, rounding at the boundary of a category, negative values, and the inputs where a calculator should decline rather than return infinity.
Authors and reviewers
Each category has a named author and, where the subject requires it, a named reviewer with relevant qualifications. Health and finance content carries a reviewer. Both are shown on the page with their credentials and a profile you can read.
While this site is being built, the personas are explicitly labelled placeholders in their own biographies. Real named people replace them before the site publishes to the public. We would rather show you an obvious placeholder than a plausible invention.
Disclaimers
Health and finance calculators carry a disclaimer, always, on every page in those categories. They are informational and are not medical or financial advice. Where a result is a prompt to talk to a professional rather than a conclusion, the page says that in plain words instead of burying it.
Advertising and independence
The site is funded by advertising. Advertisers have no input into which calculators exist, what they say, or what any result is. Ads are never placed inside a result area, and never load before you consent to the cookies they use.
Corrections
We fix errors rather than arguing with them. If you find one, tell us and include the values you entered. Substantive corrections to a calculator’s method or a formula are noted on the page.