Methodology
Formulas and sources
Each calculator page states the formula it uses and walks through at least one worked example. Where a result depends on an outside rule, such as a published grading scale, the page names it and links to the source, with the date it was checked.
Testing
The math for every calculator is written as a separate function with its own automated unit tests. The tests cover normal cases, edge cases such as boundaries and impossible inputs, and the worked examples shown on the page. The site is only published when every test passes and every internal link resolves.
Rounding
Calculations use full precision. Results are rounded to two decimal places only when they are displayed.
Privacy
Calculators run in your browser. Your entries are not sent to the site. See the privacy policy.
Updates and corrections
Each page shows the date it was last updated. Changes are recorded in the site’s version history. Sources with dated data are reviewed on a schedule. To report an error, email [email protected].