Methodology

How our calculators are built, tested and kept honest.

Where the formulas come from

We use standard, citable methods: amortization mathematics for loans and mortgages, WHO adult categories for BMI, compound-interest formulas from any finance textbook, and published engineering references for construction and electrical tools. When a topic has competing conventions (nominal vs. effective rates, US vs. metric rounding), the page states which one it uses and why.

How the calculators are checked

We're building out an automated test suite that runs each calculator against a fixed set of inputs with independently derived expected outputs. That work is in progress and is being rolled out category by category, starting with electrical and payroll — the places where a wrong number does the most damage. Coverage is not yet complete across every calculator on the site, and we'd rather say so than imply otherwise.

Alongside that, the following apply today:

  1. Published formulas. Methods are taken from citable published sources rather than invented, and the page names the convention it follows where more than one exists.
  2. Stated limits. Where a formula is known to break down — BMI for athletes, average rates on variable loans — the page says so on the page instead of implying precision it doesn't have.
  3. Cross-checks in the UI. Where possible the page shows its own verification — the percentage calculator displays the swap-trick check; the BMI page shows the inverse healthy-weight calculation.
  4. Unit conversions. Metric ↔ US conversions use full-precision factors (e.g. 1 lb = 0.45359237 kg) and only round at display time.

What the results are — and aren't

Our tools produce estimates for education and planning. They are not financial advice, medical advice, or a substitute for a professional who can see your full situation. Lenders quote different rates; clinicians interpret BMI in context; engineers size cable for the actual installation. Use our numbers to understand the shape of a decision, then verify the ones that matter.

Privacy as an engineering rule

All computation is client-side JavaScript. We have a hard site rule: your inputs never leave your device — the math runs inside the page, there is no server round-trip to get your answer, and no analytics beacon ever carries what you typed. Fonts are self-hosted rather than pulled from a CDN. There is no advertising here today; if it is ever added, it will sit in fixed slots that never cover your answer and never receive anything you enter — the funding rules spell out exactly what ads may and may not do. What you type stays on your device, full stop. Details in the privacy policy.

Corrections

If you find an error, report it with the inputs you used and the result you expected. Confirmed fixes are shipped promptly. We'd rather be corrected than be wrong.