Calculation methods & sources

Each calculator displays the equation it implements. Worked examples use the default inputs and can be reproduced directly on the page.

Measurement and body metrics

• CDC: BMI formulas and frequently asked questions
• NIST: Revised unit conversion factors

National Cancer Institute: Body surface area equations (PDF)

Financial models

Loan payments use the standard fixed-rate annuity equation. Compound interest uses the nominal annual rate and the selected compounding frequency. These tools do not retrieve lender quotes, current market rates or tax rules.

Estimates and assumptions

Engineering, health, training and resource-use models are simplified estimates. Their limits are described on the relevant calculator page. They do not replace individual professional assessment.