How we check calculations

Each dedicated calculator explains its inputs, formula, assumptions, and display rounding. References link to the textbook publisher or educational institution so you can inspect the method.

Calculation checks

Our automated checks compare known examples, alternative calculations, inverse calculations, and mathematical relationships. They also exercise zero rates, invalid inputs, and other boundary cases. Tests use the formula code served by the site. The homepage expression engine has separate precedence and scientific-notation regression cases.

Passing tests is not a guarantee that every result is correct. Financial projections use simplified assumptions, including constant rates and no lender-specific fees. A review date records a change or verification of the page; it is not a claim of an independent professional audit.

References and conventions

Where more than one convention is possible, the page identifies the one used. Monthly contributions in the interest tool use an equivalent monthly rate. Percentage changes from negative values use the magnitude of the starting value. Intermediate display values may be rounded while calculation precision is retained.

Corrections

Report a reproducible error with the calculator, inputs, actual result, expected result, and any supporting reference. Reports should avoid personal or financial account information. Confirmed calculation errors are corrected with a regression test and an updated review date. We do not promise a response time.