Calculators for decisions that actually matter

Free, no-signup tools for the money and health questions people actually agonize over — should I get solar, which debt do I pay first, can I afford this house, how much should I be eating. Every calculator shows its work: the formula, a worked example, and what the result does and doesn't mean.

Financial calculators

Health calculators

Why these tools exist

Most calculator sites give you a number and no context. That's a problem, because the number is the easy part — the hard part is knowing whether the assumptions behind it fit your situation. A solar calculator that assumes 4% annual electricity inflation will tell a very different story than one assuming 1%, and neither will mention it.

Every tool here states its assumptions out loud, shows the formula it uses, and walks through a worked example with real numbers. If a result depends heavily on an input you're guessing at, the page says so. And where a calculator genuinely can't answer the question — like BMI for muscular people, or affordability rules for irregular income — the page tells you that too, instead of pretending.

The site is free and supported by advertising. There are no accounts, no email capture, and nothing is stored — every calculation runs in your browser and disappears when you leave. More about the site and where the formulas come from is on the about page.

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