Accuracy and sourcing
Every calculator is built from an established, published formula or a recognised standard. We prefer primary sources — the issuing body, the peer-reviewed paper, or the official guideline — over secondary summaries. Each calculator page lists its references so you can verify the method yourself.
- Health and fitness tools are based on recognised standards such as WHO, NHS, CDC, ACOG and ACSM, and on peer-reviewed sports-science literature.
- Financial tools use standard amortisation mathematics and cite bodies such as the CFPB, Federal Reserve and equivalent national authorities.
- Construction and engineering tools use standard densities, coverage rates and constants, with sources noted.
How we describe our tools
We reserve terms like "evidence-based" for tools genuinely grounded in scientific literature (for example, health and fitness calculators). For everyday tools such as tips, discounts or unit conversions, we describe them as transparent calculators built from established formulas, rather than as scientific instruments.
AI-assisted interpretation
Some pages offer an optional AI-written interpretation of your result. This layer is grounded: it may only use the calculator's own computed output and its vetted reference material, and every number it states is checked against that material before display. If a claim cannot be supported by the page's own sources, it is not shown. AI interpretations are labelled as general information, not professional advice.
Review and dating
Pages carry a "last reviewed" date. Rules-based financial data (such as tax brackets) is labelled with its applicable year and jurisdiction, and country mortgage benchmarks are re-verified on a weekly schedule. When we become aware that a figure is out of date, we correct or clearly label it — see our Corrections Policy.