A single-developer project that grew out of being tired of calculator sites where the answer is buried under three paragraphs of filler and four ad blocks. The aim here is the opposite: the number first, the explanation underneath, and enough sourcing that you can check the work.
Why this site exists
Most questions that bring people to a calculator are small and practical. How much of this loan is interest? Is this heart rate normal for my age? How many tiles for this floor? Those questions deserve a direct answer, not a page that makes you scroll past an essay to reach a form.
So every page here is built the same way: the tool first, then a short explanation of what the formula actually does, then a worked example with real numbers, then the caveats. If you only need the number, you are done in ten seconds. If you want to understand the number, keep reading.
How the calculators are built
Everything computes in your browser. There is no server doing the arithmetic, which means the site is fast, works offline once loaded, and never sees the salary or the medical figure you typed.
- Formulas come from published, checkable sources — for health tools, the standard clinical formulas and their original authors; for tax and benefit tools, the statute or the tax authority's own guidance.
- Where a calculator encodes one country's law, the page says which country. Polish VAT, family benefits and social contributions are the main examples.
- Where a figure is an approximation rather than a live value — currency rates most obviously — the page says that too, rather than implying a precision it does not have.
- The site is open about its limits. A calculator that cannot see your credit history should not pretend to quote you a mortgage.
When something is wrong
Calculators have bugs, laws change, and a formula that was right in 2024 can be wrong in 2026. Corrections are the most useful mail this project gets, and they are acted on rather than filed.
If a result looks wrong to you, it is worth telling me. Send the inputs you used, the result you got and the result you expected, to contact@fastcalco.com. Being told a number is wrong is more valuable than being told the site is nice.
Who writes this
The site is built and maintained by one developer based in Poland. That is why the Polish-law calculators are the most detailed ones — they are the ones I needed myself — and why the site exists in six languages rather than one.
It is not a media company, there is no editorial team, and nothing here is sponsored content. When a page recommends checking with an accountant or a doctor, that is not a disclaimer template; it is the honest limit of what a formula can tell you.
How it is paid for
Advertising, and nothing else. There is no paid tier, no affiliate links inside the calculators, and no data sold — there is no data to sell, since nothing you type leaves your device. Ads are placed below the tool rather than above it, because a page that makes you scroll past an advert to reach the thing you came for is the problem this site was built to avoid.
Languages
The site is published in English, Polish, German, French, Spanish and Italian. Translations are reviewed rather than machine-dumped, but they are not the work of professional translators, and a phrase will occasionally read stiffly in a language that is not my own. If you spot one, the same address works.
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