Our Methodology

Every calculator is built on a formula that is publicly documented — a published standard, a textbook method, or an arithmetic definition. We do not invent proprietary formulas. Examples:

• Health: BMR uses the Mifflin-St Jeor, Harris-Benedict, and Katch-McArdle equations. TDEE applies standard activity multipliers to BMR.
• Finance: Loans and mortgages use standard amortization math (the same math as a spreadsheet's PMT function). Compound interest uses the standard compounding formula, with inflation adjustment as an optional input.
• Math: Statistics, percentages, and algebra use standard definitions used in school and university curricula.
• Marketing: ROAS, CAC, CPM, CTR and similar ratios are industry arithmetic — the ratio itself, not an estimate.

Where an industry has several accepted methods (for example, three BMR formulas), we offer each method explicitly rather than silently picking one.

Before a calculator ships, its default values and worked examples are checked three ways:

• The calculator's own output for the example inputs.
• A manual calculation, done independently step by step.
• A spreadsheet (Excel or Google Sheets) using the equivalent built-in function where one exists — for example PMT for loans.

Worked examples on each page are then recalculated whenever the page is updated. If you find a number that doesn't match your own calculation, tell us (see corrections below) — the three examples we got wrong before fixing them in October 2026 are exactly why this check exists.

Cases and scenarios on our pages are illustrative: composite examples built from common patterns, not data from identified companies or patients. We do not present invented case studies as real ones. Where a page gives industry benchmarks, we name the source or describe where the range comes from — and remind that real margins and rates vary widely, so treat ranges as guides, not rules.

Statistics quoted from studies link to an accessible source where possible. If we can't verify a number, we don't publish it.

Each category has a named reviewer whose profile (with the topics they cover) is on our About page. Reviewers check that the formula, explanations, and examples are consistent and that nothing on the page oversells what a calculator can tell you.

We don't claim clinical, legal, or licensed credentials that our reviewers don't have. Where a topic genuinely needs a professional (medical dosing, legal settlements, tax), the page says so and links to the relevant disclaimer.

Pages show a visible “last updated” date. The date changes only when the page's content actually changes — we don't stamp every page with the same timestamp. When a formula, benchmark, or example changes, the change is made across the page (text, FAQ, and metadata) in the same edit.

Found an error? Email supportgmcalculator@gmail.com with the page URL and what you calculated. Correct takes priority over publication: we fix first, then confirm. Errors in health or finance numbers are treated as urgent.

The site is free and always will be. It is supported by ads, which never influence how a calculator works or what a page recommends. We do not sell links, publish paid reviews, or accept content in exchange for money.