Where AI was used, and where it was not

No AI runs when you use a calculator

Nothing you type is sent to a language model, or anywhere else. There is no AI in the product — only ordinary, deterministic arithmetic running in your browser.

This is worth being precise about, because “AI-powered calculator” has become a common thing to claim and it would be a bad idea. Language models are probabilistic; they are the wrong tool for working out a mortgage payment. The formulas here are written as plain functions, and the same inputs always produce the same output.

Those functions are covered by automated tests, including regression tests that check our result against a figure published by someone else — so a $300,000 loan at 6.5% over 30 years has to come out at the payment the published amortisation tables give, or the build fails.

AI helped write the code

The site was built with substantial help from an AI coding assistant: the components, the styling, the test suite and much of the prose, including this page, were drafted with AI assistance and then reviewed, corrected and tested by a person.

Every change has to pass type checking, linting, the full test suite and a production build before it ships. A green build is not proof the arithmetic is right, so calculators are also checked by hand against figures worked out independently.

The images are AI-generated

None of the photographs on this site are photographs. The image across the top of the home page, the tile on every calculator, and the picture heading each article were all produced by AI image models. The colour treatment and the calculator tiles were then finished in code so they match the palette exactly, and the logo mark began as an AI-generated concept that was redrawn by hand as vector geometry so it stays sharp at every size.

We mention it because a picture of a real-looking street, or an office, or a loaf of bread invites you to assume a camera was involved, and none was. No real place, person or property is depicted anywhere on this site, and nobody in any image exists.

Published figures are checked by a person

Some numbers here are not arithmetic but facts published by an authority: federal tax brackets, the standard deduction, the Social Security wage base, ingredient densities, oven temperature charts. These go stale, and getting one wrong would quietly corrupt every answer that depends on it.

So the rule in this project is explicit: a figure may be marked verified only when a human has opened the authority’s own page and checked it, on a recorded date. Not because it looks familiar, not because several websites agree, and not because a model said so. An AI assistant may draft a new year’s data and find the source. It may not mark that data verified.

Exchange rates are machine-refreshed, and dated

Currency rates are the one exception to human verification, because they change daily and a signature would be stale before it was committed. They are fetched automatically from the European Central Bank each time the site is built, and stamped with the date the ECB published them — currently 2026-08-21.

That date is shown on the converter, and the page warns you when the snapshot is getting old. They are reference rates: useful for understanding roughly what something costs, and not the rate any bank or card will give you.

Why disclose any of this

A calculator earns trust by being right and by being clear about what it does not know. Telling you that AI wrote much of the code, that AI made the pictures, and that AI is specifically not permitted to certify a tax bracket is part of the same commitment as printing “does not include state tax” next to a take-home figure.

If you find a number here that is wrong, we would genuinely like to know: hello@plainnumber.com.

Related

See the Privacy notice for what the site does with your data — nothing — and the Terms for the estimates-not-advice boundary.