How we build and verify our calculators
Every number on this site — every formula, coefficient, threshold and reference-table value — goes through the same process before it is published. This page explains that process.
1. Published formulas only
We never invent our own equations. Every calculator implements a formula that was published and is in established use: Mifflin-St Jeor for resting calories, the U.S. Navy circumference method for body fat, Boer and Hume for lean body mass, Epley and Brzycki for one-rep max, Riegel's endurance model for race prediction, Karvonen for heart-rate zones, and WHO/CDC classifications for BMI and weight ranges. Each calculator page names the formula it uses.
2. Primary-source research
Before a tool is built, we research each formula and threshold against the most authoritative source available — the original paper where practical, otherwise guidance from bodies such as the CDC, NHS, NIH, WHO and ACOG, or standard references such as the Compendium of Physical Activities for exercise energy costs. Values are recorded together with their sources.
3. Independent fact-checking before launch
The research then goes through a separate adversarial review that tries to prove it wrong: every coefficient is re-checked against its primary source, and worked examples are recomputed by hand to confirm the maths. This step has real teeth — pre-publication checks have caught and corrected genuine errors before they went live, including an outdated MET value for yoga, a lean-body-mass reference table with the wrong coefficients, and a race-prediction table that was too optimistic. Nothing ships until the disputes are resolved against the evidence.
4. Testing the implementation
Once coded, each calculator is tested against hand-computed examples and checked across metric and imperial units, so the tool you use matches the verified formula exactly.
5. Reviews and updates
Health guidance evolves, and so do our tools. Each page shows when its content was last updated, and we revisit calculators when the underlying guidance changes. Results are checked against CDC, NHS and NIH guidance; where a health claim appears in our guides, the source is cited so you can read the science yourself.
Corrections
If we get something wrong, we want to fix it quickly. Spotted a value that doesn't match its source, or a result that looks off? Tell us — include the calculator, the numbers you entered and what you expected, and we'll investigate against the primary source and correct the page if needed.
What we are not
We are an educational reference, not a medical service. Our results are population-level estimates, clearly labelled as such, and are no substitute for advice from a qualified healthcare provider who knows your individual situation. Read more on our about page.
Reviewed against CDC, NHS and NIH guidance. Estimates for education — not medical advice.