Sources & methodology

For official units, legal rules and regulatory thresholds, the relevant standards body or public authority is the first place to check. For a published scientific equation, the original paper and its stated population matter.

Textbooks and established identities support stable mathematical relationships. Independent cross-checks help reveal differences in units, rounding, definitions and timing conventions.

The resources below are places to find primary standards and published literature. They are not a claim that every calculator uses every resource, and their names or logos do not imply partnership or endorsement.

World Health OrganizationHealth reports and published reference methods.PubMed / National Library of MedicineFind original biomedical papers and their study populations.BIPMThe International System of UnitsSI unit definitions and measurement conventions.NISTFundamental physical constantsCODATA values, uncertainty and scientific reference data.

Check the unit system, compounding frequency, date convention, reference population and treatment of boundary values. Two tools can use different valid conventions and therefore return different results.

We aim to make these choices visible in labels, formulas and examples. A rounded display can sit on a threshold even when the underlying, unrounded value falls just below it.

A research association is not an individual prediction. A screening threshold is not a diagnosis. An equation validated in one population may not apply to another.

Tax, interest, regulations and clinical recommendations can change. Check the applicable date, jurisdiction and original source before using a result for a consequential decision.

A reference-based notice means published sources informed a method or explanation. A named expert review is a separate page-specific assessment, published through our review process.

Neither a source logo nor a review badge is a guarantee that a result is suitable for every person or circumstance.

Send the calculator URL, input values and units, the result shown and the primary source or worked calculation you believe should be used. Let us know if the issue concerns the formula, the source, a boundary value or the explanation.