Our methodology

Standard, published formulas

Every calculator uses a formula that is publicly documented — from textbooks, international standards, or widely used professional practice. We don't invent private formulas, and we don't adjust results to look nicer.

Where more than one formula is in common use (for example, estimating resting metabolism), we pick the one with the strongest evidence base — the Mifflin–St Jeor equation in that case — and say so on the page.

Assumptions in plain view

No model matches reality exactly, so every calculator lists its assumptions next to the result: fixed interest rates, no taxes or fees, population-average health formulas, calendar rules, and so on.

If an assumption makes a result a rough estimate rather than an exact figure, the page says that explicitly in the limitations section.

Worked examples you can verify

Each calculator page walks through at least one fully worked example, step by step, so you can confirm the method with pen and paper before trusting it with your own numbers.

The worked example is computed by the same code that powers the live tool — not written by hand — so the example and the calculator can't drift apart.

Testing and review

The calculation engine is covered by automated unit tests that check known values, boundary cases (zero, negative numbers, leap years), and error handling for invalid input.

Pages carry a “last reviewed” date. When we re-check a page against its sources, the date is updated. Errors reported through the contact form are investigated and corrected, and the review date reflects the fix.

Privacy by design

All calculations run entirely in your browser. The numbers you type are never sent to our servers, logged, or stored. The only data we receive is what you deliberately send us through the contact form.