Numeros publishes free calculators that show their working. Every tool has the formula it used, a worked example, and a plain statement of what it cannot tell you — because a number you cannot check is a number you should not act on.
400+calculators
Across finance, health, mathematics, physics, engineering, construction, business, education, date and time, lifestyle, converters and generators.
0accounts, gates or limits
No sign-up, no email wall, no usage cap, no premium tier. Nothing you type is sent anywhere — every calculation runs in your own browser.
100%formulas shown
Each page states the equation it uses and works an example through it, so you can verify the result rather than trust it.
How a calculator gets published
Every tool on this site goes through the same process before it goes live. It is deliberately slower than publishing quickly, and it is the reason there are 400 tools rather than 4,000:
- Find what the existing tools get wrongBefore anything is built, the leading calculators for that search are used and checked. Often they agree with each other and are all wrong in the same way — reporting months as days divided by 30.44, ignoring public holidays in a working-day count, or assuming weekly overtime in a state that uses a daily rule.
- Take the formula from a published sourceEquations come from the paper, standard or regulation that defined them — Mifflin-St Jeor from the 1990 American Journal of Clinical Nutrition, curing figures from ACI 308R, APR from Regulation Z. Not from another calculator, and not from memory.
- Verify against a hand-computed referenceThe code is then run against worked examples from the source itself. More than once this has caught an error in the reference values rather than in the code — which is the point of doing it in that order.
- Test the edges, not just the middle29 February. A shift crossing midnight. A waist measurement that makes the Navy body-fat formula return a negative number. Most calculator bugs live at the boundaries, and most calculators return the nonsense without comment.
- Write down what it cannot doEvery page says where the method fails. Tape measurements are accurate to three or four points; activity multipliers have no real evidence base; a projection assuming a steady 7% describes something markets have never delivered.
- Say when a professional is neededAnything touching money, health or structure carries a plain statement that the figure is an estimate and who to ask instead.
Who builds this
Numeros is built and maintained by a small independent team rather than a publisher or a marketing agency. Nobody here is a doctor, a financial adviser, an accountant or a structural engineer, and no page pretends otherwise — which is exactly why every tool cites the standard it implements and says plainly when the question needs someone qualified.
The expertise this site does claim is narrow and real: reading a published formula correctly, implementing it without introducing arithmetic errors, testing it at the boundaries where it breaks, and describing its limits honestly. That is a smaller claim than most calculator sites make implicitly, and it is one that can be checked — every page shows its working precisely so that you can.
What this site will not do
Collect your calculations
Every calculation runs in your browser. Nothing you enter is transmitted, stored or logged — which you can confirm in your browser’s network panel. Analytics and advertising scripts are a separate matter, covered below.
Gate anything
No tool requires an account, an email address or a subscription. There is no premium tier and no usage limit.
Give advice
Estimates, not recommendations. Where a decision has real consequences, the page says so and names the kind of professional to ask.
Hide the method
No tool asks you to trust a number without showing where it came from. If the formula is not on the page, that is a defect.
How this site is paid for
Numeros is free to use and costs money to run, so it carries advertising and some affiliate links. Saying so plainly matters more than the revenue does:
Display advertising
Pages carry Google AdSense. Those scripts set cookies and see your visit; the calculators themselves still send nothing. Ad blockers do not break any tool on this site.
Affiliate links
A small number of pages link to products or services and may pay a commission. Every one is marked rel="sponsored" and disclosed on the page it appears on.
What money does not buy
No advertiser sees a calculator before it is published, chooses what gets built, or influences a result. A commission never changes a recommendation or a number.
Analytics
Google Analytics records which pages are visited, so the rebuild queue follows what people actually use. It does not record anything you type into a calculator.
If a page recommends something and stands to earn from it, the page says so where you can see it — not in a footer, and not after the recommendation. Most tools here have no commercial link at all, and none has one that changed what it calculates.
Corrections
Errors happen, and a wrong calculator helps nobody. If you find one, please say so — include the numbers you entered and what you expected, and it will be checked against the source and fixed as quickly as it can be verified.
Corrections are made to the page itself rather than announced separately. Where a change alters a result rather than the wording, the page is updated and the modification date changes with it.
Where to start
The full index lists every tool, or browse by category:
- Financial — mortgages, loans, tax, retirement, investment
- Health — BMI, calories, body composition, fitness
- Mathematics — algebra, geometry, statistics
- Business — margin, ROI, payroll, valuation
- Date & Time — durations, working days, age
- Converters — units, temperature, pressure, volume
- Generators — PDF tools, Markdown, passwords, QR codes
See also the disclaimer, the privacy policy and the terms of use.