Where the formulas come from
Each calculator states its formula on its own page, in words and symbols, along with what every variable means. Where a figure is set by law or by a standards body. A tax bracket, a superannuation guarantee rate, a repayment threshold, a BMI cut-off, a concrete bag yield. The page lists the source it came from and the year that figure applies to.
Where a calculation is a widely used estimate rather than a legal rule (body fat from tape measurements, calorie burn from activity multipliers, breach cost by industry), the page says so in its assumptions and names the method used.
What is checked automatically
- Every calculator runs on every build with its default inputs, and again with zero, negative and extremely large inputs.
- A result containing NaN, Infinity or an undefined value fails the build. Calculations that cannot produce a sensible answer must return a plain-language message instead.
- Charts, step-by-step working, comparison tables and what-if scenarios are executed too, and are bounded so no input can make a page hang.
- Internal links are verified: a calculator cannot reference a related tool or guide that does not exist.
- Content depth is enforced. A page without worked examples, explained outputs, stated assumptions, sources and questions fails the same build gate.
Review cadence
Every calculator carries a last-reviewed month and, where relevant, the data year its figures belong to. Both are shown on the page and published in the page's structured data so search engines and assistants can see how current it is.
Australian tax, superannuation and study-loan figures are reviewed each July when the financial year turns over. United States federal figures are reviewed when the annual inflation adjustments are published. Health guidance is reviewed when the issuing body updates it. Anything else is reviewed at least once a year.
Corrections
If a number here is wrong, the fix is a code change with a test, not an edit to a sentence. Report it through the contact page with the calculator name and the inputs you used, and the correction ships with the next build along with an updated review date.
What these tools are not
They are estimates built from the inputs you provide. They do not know your full circumstances, they do not replace advice from a professional who does, and they are not a substitute for an official assessment from a tax authority, lender, insurer, regulator or clinician.