How We Build and Check These Pages

CalcPerch is made of numbers, and a number is only worth as much as the method behind it. This page describes where the figures come from, what is checked automatically before anything is published, what we deliberately do not do, and how to tell us when something is wrong.

Where the numbers come from

Every rate, threshold and conversion factor on this site is taken from the body that defines it, not from another calculator site. In practice that means:

• Tax figures — federal brackets and the standard deduction from the IRS; the Social Security wage base from the SSA.
• Unit conversions — the exact defined factors published by NIST and the BIPM. Where a factor is exact by definition rather than measured, we say so.
• AI model prices — each provider's own published pricing page. Never a third-party summary, and never an aggregator, both of which lag real price changes by weeks.
• Lending and consumer-finance definitions — the CFPB and Regulation Z, which is what actually defines terms like APR.

Pages that make a factual claim carry a "Sources" block naming the specific documents used. Pages that are pure how-to — how to merge a PDF, how to pick an image format — do not, on purpose. Attaching official-looking citations to a page that does not need them is a way of borrowing authority, not demonstrating it.

What gets checked before anything is published

The site is a set of static files built by scripts, and the build refuses to complete if certain things are wrong. These checks run on every build, not on a schedule someone has to remember:

• Link integrity — every internal link on every page is resolved against the files on disk, and one broken link fails the build. No figure is quoted here on purpose: an earlier version of this page said "4,296 internal links across 92 pages", which was true when written and wrong within a day of the site being restructured. A page about checking things should not carry a number that nothing checks.
• Price consistency — a model's price appears on several pages. A checker compares all of them against the single source table and fails the build if any two disagree, which is the failure mode that actually happens when prices change.
• Shared formulas — where a reference page and a calculator compute the same thing, they are generated from the same constants rather than maintained separately, so they cannot drift apart.

The "Last reviewed" date at the foot of each page is content-addressed: it moves when that page's content actually changes, and not otherwise. A rebuild with no edits does not re-date anything. That is deliberate — a date that advances every day tells you nothing.

What runs in your browser, and what we collect

Every calculator and every file tool on this site runs entirely in your browser. Images you crop, PDFs you merge, text you compare, and numbers you type are processed locally and never uploaded. This is not a privacy promise you have to take on faith: open your browser's network tab and use any tool on the site — apart from the two exceptions named below, there is no request carrying your data. The pages themselves are static files.

The two exceptions are stated where they apply: the URL shortener necessarily stores the link you create, and the background remover downloads a machine-learning model to your browser the first time you use it — the model comes to your device, your photo does not leave it.

For traffic figures we use Cloudflare Web Analytics, which runs at the network edge rather than in your browser — there is no analytics script on any page here, no cookie, and no fingerprinting, and it cannot follow you to another site. Advertising is Google AdSense, which does set cookies; what those do and how to opt out is set out in the privacy policy. Those two are the only third parties involved in ordinary browsing. The URL shortener additionally sends the address you paste to is.gd (or v.gd, or TinyURL) — that is what shortening a link means, and it is the one place your input leaves your device.

What we do not do

Some of this is worth stating plainly, because a lot of calculator sites do the opposite:

• We do not mass-generate pages. In July 2026 this site carried 122 programmatic pages — one per salary figure, one per unit pair — that differed only in their numbers. They were removed rather than expanded. If a page cannot say something the neighbouring page does not, it should not exist.
• We do not pad. Where a topic is genuinely short, the page is short.
• We do not give financial, legal, tax or medical advice. The tools compute; they do not recommend. A take-home pay estimate is not a tax return and a BMI figure is not a diagnosis, and both pages say so.
• We do not invent precision. Where a figure is an estimate — a take-home column using a placeholder state rate, say — the page says which parts are assumed rather than calculated.

Corrections

If a number here is wrong, we would rather know. Send the page and what you expected to contact. When a correction is made, the page's content changes, so its "Last reviewed" date moves with it — the date and the fix are the same event, not two separate claims.

Errors we have found ourselves are fixed the same way. As one example: the salary pages used to estimate take-home as a flat 68–80% of gross, applied at every income. US income tax is progressive, so a flat share is wrong in a way that mattered most at the bottom — at a $30,000 salary the real figure is about $26,285, while the pages claimed $20,400–$24,000, a range entirely below the truth. That was replaced with the actual bracket calculation.

Who maintains this

CalcPerch is an independent site, not a division of a larger company. It is built and maintained by one developer, who writes the code, checks the arithmetic, and reads every message sent to the contact address — there is no content farm and no outsourced writing behind it. Nothing on the site is sponsored, and no tool or provider pays for placement or for a favourable comparison — where an AI model is described as the cheapest option for a workload, that is what the arithmetic on the cost benchmarks page produced, and the assumptions behind it are published so you can rerun it. Revenue comes from advertising, which is disclosed in the privacy policy and has no bearing on what the calculators output.

More about the site's purpose and history is on the about page.