This policy governs everything published on this site. It exists so readers, advertisers and regulators can see how our content is made and held to account.
Who writes this site
4Calculators is written and published by one person, Michael A. Levy, using AI — Claude Opus 5, directed page by page. There is no editorial team. An earlier version of this policy described one, and that was wrong; it has been corrected here and on the About page.
How a calculator is produced and reviewed
Stated plainly, because on a library of 1,292 pages the honest answer is more useful to you than a reassuring one. Every calculator goes through four stages:
- Specification (human). The governing formula, the standard or text it comes from, the inputs and their units, the edge cases, and the test vectors the page must satisfy are decided and written down first.
- Drafting (AI). Claude Opus 5 writes the calculation code, the article, the worked example, the reference table and the FAQs against that specification.
- Review (AI, then machine). A separate AI pass, run independently of the one that wrote the page, checks it for unattributed numbers, claims that invert at a sign or threshold change, and figures that were typed when they should have been computed. The build then validates every page structurally and executes each calculator's test vectors in a real browser. A calculator whose tests fail is not published — that is enforced by the build, not by anyone's diligence.
- Human review (selective). Many calculators have been read and checked personally. Not all of them have. With 1,292 published pages, claiming otherwise would be false.
So: the arithmetic on this site is verified mechanically and comprehensively, and every page's formula and sources are stated so you can check them yourself. What is not claimed is that a licensed professional has reviewed each page in your field, or that a human has read every sentence of every article. Where a calculation carries real consequence, treat this site as a well-documented starting point and have the number confirmed by someone accountable for it.
Use of AI
This site is written with AI, and says so rather than burying it. The articles, the worked examples and the calculation code are drafted by Claude Opus 5 against a human-written specification, and the pages are assembled by a static site generator.
Two things follow, and both are worth knowing. AI is very good at producing a large volume of correctly structured, correctly sourced technical writing, and it is capable of producing a confident sentence that is wrong — a number that was typed rather than computed, or a claim that holds for the example given and inverts at a threshold. That second failure mode is the reason for the independent AI review pass and the test-vector suite described above, both of which exist specifically to catch it.
What AI is not used for: inventing sources. Citations point at real, named documents — a standard, a code section, a government publication, a textbook — and a figure that cannot be attributed or recomputed does not belong on the page. If you find one that is, report it; that is the class of error most worth hearing about.
Sourcing and verification
Every calculator and article is built from published, attributable sources — standards, codes, government publications, peer-reviewed literature, or canonical textbooks. Sources are cited on the page. We do not publish statistics, prices, or survey figures that we cannot attribute, and we do not fabricate citations. Where a number is a widely used rule of thumb rather than a standard, we label it as one.
Corrections
We correct errors promptly and visibly. When a calculation or a substantive statement changes, the page's updated date changes. We do not quietly rewrite results. Readers can report errors at any time via our contact page.
Advertising independence
This site is funded by display advertising. Advertising is clearly labelled and is never permitted to influence which calculators we build, what a formula says, or what a result reports. We accept no payment for favourable treatment of a product, method, or brand, and we do not publish sponsored calculators. Advertisers have no access to editorial decisions and no advance sight of content.
Scope limits
We publish estimation and educational tools. We do not offer personalised financial, legal, medical, tax, or engineering advice, and nothing on this site creates a professional relationship. Where a decision carries legal, financial, structural, electrical, or medical consequence, have your numbers verified by a qualified practitioner in your jurisdiction.