Methodology

How calculators are built

Every calculator starts from the published NHS or UK clinical method for the measure it covers. We identify the authoritative method — including its exact formula, thresholds, units and age or population scope — and record the source and version. The calculator then implements that method exactly, asking only for the inputs it requires.

Verification before publication

A calculator moves from draft to published only after it passes verification of five items: the formula, the thresholds or interpretation bands, the units, the source version, and the limitations (groups or situations where the method is not validated). The result is reviewed by a named reviewer and recorded with author, reviewer, sources and last-reviewed date.

Review cycle

Published calculators are re-checked against their sources on a regular cycle and whenever a source guideline is updated. Changes are documented in the page history and, where material, announced in the site log.

Last updated: September 2026.