About CalcLab

CalcLab (계산기랩) lives at one domain, calculab.net, and opened in July 2026. It is not affiliated with any other site that uses the same name on a different domain.

CalcLab is a free set of calculators for the arithmetic that turns up in ordinary life — hours and pay, dates and ages, units, percentages, sleep, calories. There is nothing to install and no account to create: open a page, type your numbers, and the answer is already there. It is built and maintained by one person, and this page exists so you can decide for yourself whether that is worth trusting.

Who writes these calculators

I build and run this site on my own. Nothing here is outsourced, mass-produced, or generated automatically to fill out a category. That is a limitation as much as a claim: the number of pages grows slowly, and I would rather it grew slowly than pad the site with calculators I have not checked myself.

I am not a tax adviser, an accountant, a lawyer, or a doctor. What you get here is a tool that applies published, public rules to the numbers you type — not a professional's judgement about your situation. Anything that turns on judgement (whether an allowance actually applies to you, how a contract should be read, what a symptom means) is outside what a calculator can do, and I say so on the pages where it matters rather than implying otherwise.

How a calculator gets published

A calculator that returns the wrong number has no reason to exist, so each one goes through the same four steps before it goes live.

1. Primary sources only. I do not copy figures off other calculator sites or blog posts. Rates come from whoever sets them — the annual Social Security wage base as announced, HMRC's published bands and thresholds, the standards document behind a unit or a size chart, the health authority behind a guideline.
2. A dated basis on the page. Any calculator that leans on a rate or a threshold states, at the bottom of the page, when it was last checked and against what. Last year's rate believed to be this year's is a loss you carry personally, so the date is part of the answer.
3. Automated checks on the arithmetic. Band boundaries, zero and negative inputs, values above a cap — the places calculators break — are covered by tests that run on every build. The example numbers written into the prose are checked too, so a fix to the code cannot quietly leave the explanation saying something else.
4. A real browser before publishing. A page like this still looks perfectly fine when its script has silently died, so every page is opened in an actual browser and checked for errors before release.

Written for the country, not translated

The English pages are not a machine pass over another language edition. Where a calculator depends on a national rule, each edition is written against the authority that applies to its own readers, and the answers legitimately differ.

Recommended sleep is the clearest example. The English sleep calculator judges adults against the 7 or more hours in the AASM and Sleep Research Society consensus, with the NHS figure of roughly 7 to 9 hours alongside it. Japan's health ministry guide sets the adult target at 6 or more hours; Korean public guidance says 7 to 8. None of the three is wrong — they mark different points in the same range, and each edition uses its own. The same applies to pay: the English hourly-wage calculator works in US FICA or UK PAYE, not a foreign payroll system relabelled in English.

What happens to what you type

Nothing you enter is sent anywhere. Every calculation runs in your browser, on your device, with no account and nothing stored.

There is one thing worth naming rather than hiding. A few calculators need outside data — exchange rates, metal prices — and that data is fetched once a day, when the site is rebuilt, and written straight into the page. That is why those figures are present before any script runs, and also why they are a daily reference rather than a live market feed. Even on those pages, nothing you type leaves your browser: the outside data comes in, your numbers do not go out.

When it turns out to be wrong

I fix it and I write down what was wrong. Nothing is changed quietly. Recent corrections:

• 28 July 2026 Hourly wage calculator. US FICA was applied as a flat 7.65%, which ignores the fact that Social Security stops at the annual wage base ($184,500 for 2026). The UK side was missing the 2% National Insurance band above the upper threshold, and the personal allowance taper that removes £1 of allowance for every £2 earned over £100,000. On £80,000 a year the take-home figure was out by about £545 a month. Both sides were rewritten against the published thresholds.
• 3 August 2026 Random picker. The page said the winner was drawn with the browser's secure random numbers, while the code was actually using ordinary Math.random. The code was changed to match what the page claimed — not the other way round.
• 3 August 2026 Sleep calculator. The bedtime window carried a sleep-cycle margin, which meant that lying down at the late end of a window offered as "to get 8 hours" produced under 7 hours of actual sleep. The margin was removed; the window now comes from the recommended range itself, so anywhere inside it really does meet the target.

Before you rely on a number

Every calculator follows widely used formulas and published public standards, but the results are for reference. They cannot see your filing status, the rest of your income, a local exception, or the terms of your particular contract. Where money or the law is on the line — tax, payroll, a loan — confirm the final figure with the relevant institution or a professional.

That limit is worth stating plainly. What I do is read published primary sources and turn them into arithmetic, and two things follow from that. First, interpretation is involved: statutes and official notices are prose, and turning prose into a formula takes judgement. Mine may differ from how the authority actually applies the rule, and where it does, the authority is right. Second, I cannot see your situation — and that is usually what decides the real figure.

So these numbers carry no legal force and create no contractual obligation. Do not use them as the settled basis for a tax filing, a contract, an insurance claim or a medical decision, and do not submit them as evidence in a dispute. In those places the authority's own calculation, or a professional's judgement, is the basis.

What I will not do is hide my working. Calculators that depend on rates or statutes state which source was checked and on what date at the foot of the page, so you can go to that source and check me. If I am wrong, tell us. The full disclaimer is in the Terms of Use.

How the site pays for itself

This site is free and is meant to stay that way. Hosting and the domain are covered by advertising. I try to keep the ads out of the way of the thing you came for: they should not cover a result, and they should not sit where you are about to tap. What is processed for advertising is set out in the Privacy Policy.

Contact and error reports

If a calculation looks wrong, or a source you follow has changed, please tell me. I will check it, fix it, and add it to the list above. Suggestions for new calculators, advertising enquiries and privacy requests reach the same address.

Email: calculab.admin@gmail.com

For an error report it helps enormously to say which calculator, what you entered, and what came out. Copying the address straight from the calculator screen is the surest way of all — your inputs travel in the link, so I can reproduce exactly what you were looking at.