About

A collection of free calculators, each built around one question: what a loan payment comes to, what is left of a salary after deductions, where a body mass index falls, when a pregnancy reaches full term. They cover loans and mortgages, net pay and severance in several countries, BMI and body fat, due dates, dividend tax and VAT, and everyday arithmetic. No sign-up, no paywall, nothing to install.

Below each result you will find the formula, a worked example with real numbers, the assumptions behind the calculation, the cases where it does not apply, a reference table where one helps, the questions people actually ask, and the sources. That costs more effort than it saves, but it is what lets you check the number instead of taking it on faith. A page that prints a number and stops is quicker to read and easier to rank. But a number you cannot check is a number you have to trust — so instead of asking you to trust this site, every figure comes with its source and the date it was last checked.

The arithmetic is rarely the hard part: a net pay calculation is multiplication and subtraction, a loan payment one formula. Knowing which figures are currently correct is the hard part. Rates change quietly — Korea's national pension contribution rose from 9% to 9.5% during 2026, and the earnings ceiling it applies to resets every July, so one calendar year holds two values. None of that raises an error. A calculator running on last year's rate returns a confident, well-formatted, wrong number.

So every calculator has a companion file listing the figures inside it that can go stale. Each entry records the figure, its current value, the body that publishes it, a link to the document it came from, when it was last checked, when it is due to be checked again, and why that date rather than an arbitrary one.

Entries are graded. Primary means the official page of the body that sets the figure was opened and read. Derived means no single document states the number and it was computed from two official ones — Korea's health insurance rate, where the ministry publishes only the annual increase. Secondary means it was cross-checked in specialist coverage because the primary document was out of reach.

An automated test enforces this on every build, failing it if a check date has passed or a figure in the prose no longer matches the constant used in the calculation — so nothing ships until someone returns to the source. Right now that publishing happens only on the Korean-language calculator pages, where each entry appears in a table headed (in Korean) "the figures used in this calculation"; the same table is being extended to the other four languages one at a time, so for the moment the sources and check dates are visible there first.

Some sources are out of reach, and the honest response is to record that rather than pass off a second-hand figure as an official one.

The body fat calculator is the clearest case. Its estimate uses a regression the US Navy published in 1984, whose original technical report returns HTTP 403 on the Defense Technical Information Center's server. The bands it then applies — essential fat, athlete, fitness, average, obese — come from the American Council on Exercise, whose page returns HTTP 200 but no table. So the entry is filed as secondary, its note lists every failed attempt, and it is re-checked every six months instead of yearly. The bands match what is widely republished; what cannot be done here is verify them, and the entry says so.

On 22 August 2026 the due date calculator was marking full term at 37 weeks 0 days, and had been wrong since the page was written. In 2013 the American College of Obstetricians and Gynecologists and the Society for Maternal-Fetal Medicine split a single definition of term into four: early term from 37w0d, full term only from 39w0d to 40w6d, late term, and post-term from 42w0d.

Fixing it took more than one constant: the old boundary was written into the prose, the FAQ and the reference table of all five languages. The page now shows the ACOG definition beside the local clinical convention where they differ, instead of letting one quietly override the other.

The site is written in English, Korean, Japanese, German and Spanish. What matters more than the wording is that each version follows the standards that actually apply where that language is read.

The World Health Organization puts obesity at BMI 30; the Korean Society for the Study of Obesity puts it at 25 for its own population, with a pre-obesity band from 23. Korean pages open on the Korean chart and the others on the WHO chart, with the selector visible. The German dividend page works in Abgeltungsteuer plus the 5.5% solidarity surcharge, a flat 26.375%; the Spanish page works in the progressive savings-income brackets.

An automated test flags it if the versions collapse into one another — it cannot prove any version reads well, only that five pages are not saying one thing five times.

Nothing here is tax advice, legal advice or medical advice, and nothing here knows anything about your circumstances.

A net pay calculator applies standard deductions to a salary figure; it knows nothing about your year-end settlement, a non-standard contract or a benefit you are entitled to. A due date assumes a regular cycle, while a scan measures the actual pregnancy — the scan wins. A BMI cannot tell muscle from fat. Every result here is an estimate, meant to give you a realistic figure before you speak to someone who can give you a binding one.

The site is free and carries advertising through Google AdSense. There is nothing else: no affiliate links, no sponsored calculators, no paid placements inside the text, nothing behind a login.

One placement rule is self-imposed and enforced in the code rather than by memory: no ad sits beside a calculator's inputs, buttons or links. Google's publisher policies prohibit ads immediately next to interactive elements, and there is a plainer reason — someone who clicks an ad while reaching for a Calculate button has been tricked. The ad component accepts only a short list of positions, all inside the article text.

You will also not find star ratings, review counts or testimonials. There is no review feature here, so any of those would have to be invented.

This is a static site: the pages are files, and there is no application server, no database and no account. Every calculation runs in your browser, and the values you type are never sent anywhere to be computed.

Two things qualify that, and the privacy policy covers both. Your inputs are written into the page address so a result can be shared as a link, which means sharing the link shares the values. And if you consent to measurement, the analytics tag strips the query string before reporting, so those values do not reach Google Analytics — but the session replay tool records the address as it stands, so it does receive them.

One person: a developer, working alone. Not a company, not a team. There is no editorial board and no medical or tax reviewers, and this page would be dishonest if it implied otherwise. Where a figure needed expertise that is not here, the approach has been to go to the body that publishes it, read the document, record what was read and when, and say so plainly when that failed.

A bill that has passed and a rule that is in force are two different things. The posts under Blog say which of the two they are describing, and when the order or the notice that starts a rule has not been found, the post says that as well.

If you find a figure that is out of date, an explanation that is unclear, or a calculator that should exist and does not, the contact page has the address. Corrections are the most useful thing anyone sends.