Methodology & sources

Choosing sources

We prefer primary sources that publish the rule itself: school district grading policies and handbooks, College Board guidance, documentation from learning platforms such as Canvas, university registrars, the U.S. Department of Labor, the Code of Federal Regulations and the IRS for pay and mileage rules, open textbooks such as OpenStax and NIST publications for math methods, advertising platforms’ own help pages for ad metrics, university extension publications for small-business pricing, and payment providers’ published fee pages for processing fees. Where schools or businesses differ, we use a common default, say so on the page, and make it an editable input.

Testing

Every formula lives in its own module with automated tests. Tests include hand-worked cases and the worked examples printed in the cited sources, such as a district’s published GPA example, so the calculator reproduces them exactly.

Rounding

Calculations use full precision. Results are rounded only for display: GPAs to two decimals, percentages to one or two decimals and money to the cent. Your school or accountant may round differently.

Reviews and dates

Each page shows when it was first published and last reviewed. A review re-opens every cited source, checks the figures we use, and re-runs the tests. Pages are updated when a source changes or a reader reports a problem.

Limits

The calculators cover the general case. Curves, school-specific exceptions, taxes and fees outside the inputs are not included, and the result is a planning figure rather than an official one.