A calculator is only worth using if you can trust its answer. This page explains the process behind every tool on BestCalculate so you can judge our work for yourself.
1. Research the formula
We start from authoritative, primary sources — for example, the World Health Organization's classifications for health metrics, and standard financial mathematics for loans and interest. We document the exact formula each calculator uses in its on-page explainer.
2. Implement it transparently
The calculation logic is written as small, pure functions kept separate from the interface. This makes the maths easy to audit and reuse, and keeps the tools fast because the heavy lifting happens instantly in your browser.
3. Test for correctness
Each formula is covered by an automated test suite that checks it against known values and edge cases — zero-interest loans, boundary BMI categories, order of operations, and more. A calculator does not ship until its tests pass.
4. Review before launch
Before a tool goes live it is reviewed for accuracy, clarity and accessibility. Calculator pages display the date their method was last reviewed so you know how current the information is.
5. Maintain and correct
Rules and rates change. When they do — or when a reader flags an issue — we update the tool and its explainer. If you spot something that looks wrong, please tell us; corrections are a priority.
Important limitations
Our calculators are educational tools, not professional advice. Financial, health and legal decisions depend on individual circumstances that a general calculator cannot capture. Always consult a qualified professional before making important decisions. See our disclaimer for details.