About BestCalculators

Why this exists

Most calculator sites answer a question and stop there. You get a figure with no indication of what went into it, no way to check whether the assumptions match your situation, and no explanation of what to do with the result.

BestCalculators is built the other way round. Every tool shows the formula it used, states its assumptions plainly, and is followed by a written guide to the subject. If the number matters to you, you should be able to see how it was reached.

How the tools are built

Each calculator is defined as data — its inputs, its formula, its outputs — and rendered by one shared interface. That has two consequences worth knowing about as a reader:

• The maths is testable, and tested. Every formula is a pure function with unit tests behind it, checked against worked examples. Date arithmetic, for instance, uses civil-date day counting rather than millisecond offsets, which is the difference between being right and being right except twice a year.
• Your inputs never leave your browser. The tools run entirely client-side. Nothing you type is sent to us, stored, or logged — which matters most on the tools that touch income, debt, health or pregnancy.

How the writing is done

Each tool page carries a guide written for someone who has just got a number and is not sure what it means: what the figure is used for, where the common mistakes are, and when the result should not be trusted. We would rather tell you a tool has limits than let you act on a figure that does not fit your case.

Pages carry a review date. When rates, standards or conventions change, we update the page and move the date.

What we do not do

We do not give professional advice, and we say so on the pages where it matters most — finance, health, construction and legal deadlines all have their own section in the Disclaimer. We do not ask you to register. We do not sell data. We do not gate anything behind a payment.

How the site is funded

Advertising, and nothing else. That keeps every tool free and keeps us out of the business of selling your information. Ads are supplied by third parties and their presence is not an endorsement — the Privacy Policy explains what that means for cookies, and you can decline personalisation at any time from the Cookie Policy page.

Corrections

If a result looks wrong, please tell us. A calculator that quietly returns a bad number is worse than no calculator, so corrections get priority over new features. Write to hello@bestcalculators.org or use the contact form, and tell us the tool, the inputs and the result you expected — that is usually enough to reproduce it in one go.

Contact

General questions, corrections, and press enquiries all go to the same place: hello@bestcalculators.org. We read everything and reply to anything that needs a reply.