About CalcLab

CalcLab builds clear, accurate calculators for everyday numbers — starting with heating, and expanding into health, finance and more. Every tool is free, needs no sign-up, and runs entirely in your browser: your inputs are never sent anywhere.

Our sourcing standard

A calculator is only as trustworthy as the numbers behind it. We hold every tool to one rule: no invented figures. Every formula and every coefficient traces to a documented, named source — a British or European standard, a government dataset, a regulator's published figures, or an established industry method. Where a number comes from an official body, we cite it. If we cannot source a figure, we do not ship the calculator.

Each calculator page carries a Sources & method section listing the references behind its result, and a note of when the figures were last reviewed. Prices and rates that change — energy caps, fuel prices — are dated so you can see how current they are.

How each calculator is built

Every calculator goes through the same process before it is published:

• Spec. The inputs, the formula, all coefficients and their sources, plus a worked example, are written up before any code.
• Isolated logic. The maths lives in a pure, tested function — separate from the interface — so the result is verifiable on its own.
• Locked-in tests. A known-good worked example is asserted in an automated test, so the answer cannot silently drift.
• Plain-English explanation. Below every calculator is a detailed write-up: what the number means, how to gather the inputs, common mistakes, and when to call a professional instead.

UK-focused, and honest about limits

Our launch calculators are built for the UK — UK standards, UK prices, UK construction assumptions. A calculator is an estimate, and a good one is upfront about what it does and does not model. Where a decision has real cost or safety consequences, we say so and point you toward a professional survey.

Privacy

Calculations happen on your device. Analytics and advertising Consent Mode signals are optional and off until you accept them. See ourprivacy policy for the detail.

Feedback

Spotted a figure that looks off, or a source worth adding? That is exactly the kind of correction we want — accuracy is the whole point.