Methodology

This page describes the general process used by Allcalcy. An individual calculator's page is the controlling explanation of its particular formula, assumptions, jurisdiction, and limitations.

Choosing a calculation method

We prefer methods published by government agencies, standards bodies, professional organizations, or original research. Some useful calculators rely instead on a conventional planning heuristic. In those cases, the page should call it a heuristic—not a law, clinical measurement, guaranteed outcome, or universally accepted formula.

A source can support the definition or method, but it does not endorse Allcalcy or verify a user's result. Our sources policy explains the hierarchy we use.

Implementing and testing the formula

Calculation functions are kept separate from presentation code. Tests cover representative worked examples and relevant edge cases such as zero rates, boundary dates, invalid input, unit conversion, and rounding. Property-based tests are used where broad mathematical invariants can be stated. Passing tests shows that the code follows its specified model; it does not prove that the model captures every real-world circumstance.

Money, rounding, dates, and units

Financial calculators state or demonstrate their rounding conventions where rounding can affect the result. Amortization schedules may need a final-payment adjustment to close a balance. Date tools use calendar arithmetic where calendar dates matter. Unit converters distinguish exact definitions from rounded display values, and temperature conversions use their required offsets as well as scale factors.

Jurisdiction and data dates

A currency symbol does not make a calculator valid for a particular country. Tools that depend on laws, tax years, regulatory limits, or local conventions should name the applicable jurisdiction and the date or period for which their data is current. Global tools should say when their defaults still reflect a US convention, such as a US standard drink.

Estimates and uncertainty

We report deterministic calculator output precisely enough to be useful, but we avoid presenting an uncertain model as a precise prediction. A due date, insurance-needs estimate, settlement heuristic, or investment projection can be mathematically reproducible and still differ materially from what happens in practice.

Maintenance and corrections

Source-dependent calculators are reviewed when their underlying rules or data change. Material errors are corrected in the calculation, explanation, and tests together. See ourcorrections policy for how to report a problem.

What this process cannot do

Automated testing cannot provide medical diagnosis, legal analysis, financial suitability, or professional judgment. Results depend on the inputs and assumptions shown. Verify consequential decisions with the appropriate source or a qualified professional.