Numeros is an independent library of free calculators, generators and practical guides. We aim to make results understandable through clear methods, examples, sources and limitations. Explore a calculation, compare assumptions and check what the result can tell you before using it.
400+calculators
Across finance, health, mathematics, physics, engineering, construction, business, education, date and time, lifestyle, converters and generators.
Freetools without a Numeros account
All Numeros calculators and tools are free to use, with no Numeros account or subscription required. Optional external features may need a provider account or API key and may be subject to request limits.
Clearformulas and examples
Our publishing approach emphasizes an explained method, a practical example and relevant limitations. Some tools use formulas; others use reference tables, public lookups or heuristic estimates.
How a calculator gets published
Our approach to building and improving tools focuses on the following checks. The exact method and validation depend on the tool; this is not a claim that every page has undergone independent professional review:
- Define the questionIdentify the inputs, units and assumptions needed for the task. Different payment, total-cost and working-day calculations can answer different questions.
- Use an appropriate methodPrefer relevant primary references, such as research papers, official rules and published standards. Identify the method, jurisdiction and period where they affect the result. A source citation does not imply endorsement.
- Check reference examplesCompare calculations with a worked example or another appropriate reference. Relevant checks should reflect the actual calculation and its assumptions.
- Check relevant boundariesExamples include leap days, shifts crossing midnight, empty inputs, invalid units, debt exceeding assets and unavailable external data.
- Explain limitationsMeasurements can be imprecise, activity multipliers are approximations and an assumed investment return is not a market forecast.
- Identify decisions needing further guidanceFinancial, health, safety, legal and religious questions may require a qualified professional who can assess the circumstances.
What a checkable answer looks like
Consider a home loan payment. The principal, interest rate and term produce a payment estimate, but taxes, insurance, fees and changes to the rate can alter what you actually pay. The formula answers a defined question; it does not describe every cost of owning a home.
Try a scenario, then check its limits
Start with the Mortgage Calculator, compare housing options with the Rent vs. Buy Calculator, and verify the figures against your lender's current documents. That is how a result becomes useful rather than just precise-looking.
- Inputs: amount, rate, term
- Method: repayment formula
- Scope: stated costs and assumptions
- Decision: verify the real offer
Sources, dates and precision
Use the right source
A regulation, scientific paper or published standard is preferable to copying another calculator's output. Where a tool depends on a jurisdiction or method, the page should name it.
Check changing inputs
Tax thresholds, exchange rates and legal rules can change while the arithmetic stays the same. Check the data date and location before relying on a result.
Report uncertainty
Rounded inputs, measurements and projections do not justify unlimited decimal places. A responsible tool should explain the assumptions behind a precise-looking estimate.
For the sitewide approach, read the Numeros methodology. For the exact method, use the sources and limitations on the tool you are using.
How to use a result well
Start with the right question
Choose the tool whose inputs and units match your task. A payment calculator, an APR calculator and a total-cost comparison answer different questions.
Change one assumption
Try a realistic range for an uncertain input, such as a rate, material waste percentage or activity level. If the answer changes sharply, that uncertainty matters more than another decimal place.
Verify before acting
Use an official document, current quote or qualified professional for decisions involving money, health or safety. Keep the tool's stated limits alongside its result.
Looking for background first? The Numeros blog explains selected calculations in context and links back to the relevant tools.
Who builds this
Numeros is researched, built and maintained by one person, as explained in our Methodology. The byline identifies the publisher, not a claim that a doctor, financial adviser, accountant or structural engineer reviewed a tool. A tool should name the relevant source and say when a question needs someone qualified.
Our focus is implementing and explaining methods, checking relevant examples and improving tools when problems are identified. This does not guarantee that every result is correct, current or suitable for a particular decision. Numeros is not affiliated with the organizations cited as sources unless a specific relationship is expressly disclosed.
What to expect when using Numeros
Browser processing and privacy
Many calculations run locally. Some features send entered text, queries, domains or optional location information to external services; some save drafts, preferences or API keys in your browser. See the privacy policy and the individual tool page.
Free access
Numeros does not charge for its calculators or require a Numeros account. External services can have their own accounts, API keys, charges and limits. Access to a feature is not guaranteed to be uninterrupted.
Information and estimates
Tools provide information and computational assistance, not personalized professional advice. Review the Disclaimer before relying on a result for an important decision.
Explain the method
Look for the method, inputs, examples and limitations on the page. If an explanation is missing or unclear, report it so we can review and improve it.
How this site is paid for
All Numeros calculators and tools are free to use. Google AdSense advertising and affiliate commissions help cover the costs of running, maintaining and developing the site, and support the work behind it. You do not need to click an advertisement or make a purchase to use a tool:
Display advertising
Display advertising is served through Google AdSense. Advertising technologies may use cookies and collect usage information as described in the privacy policy. The calculator result must not depend on viewing an ad.
Affiliate links
A small number of pages link to products or services and may pay a commission. Commercial links should be disclosed near the recommendation and marked appropriately, including rel="sponsored" where applicable.
What money does not buy
A referral commission does not change a calculator's mathematical result. An advertisement or affiliate link is not a guarantee that a product is suitable for you; review the provider's terms and pricing before proceeding.
Analytics
Site analytics help us understand which pages are visited and which tools need improvement. Calculator input values should not be included in analytics events; details of data collection belong in the Privacy Policy.
Using an affiliate referral is optional. Where an eligible referral leads to a qualifying action, Numeros may earn a commission. Refer to the visible disclosure on the relevant page and our Privacy Policy for advertising and referral tracking.
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 on the affected page. Material changes to calculations should be reflected in the explanation and page update information. There is no guarantee that every reported issue can be resolved immediately.
Help us reproduce an error
Send the page URL, the inputs, the output and the result you expected. Avoid including account numbers, medical records or other sensitive information. A reproducible case lets us compare the code with its stated formula and source.
How a reported issue is reviewed
- Reproduce it. Check the stated inputs, units, browser and selected options.
- Trace the cause. Separate an arithmetic bug from an outdated source, a missing assumption or unclear wording.
- Correct the page. Recheck a worked example and the relevant edge case; explain a material change to the result on the affected page.
There is no promise that a report can be resolved immediately, but a reproducible example makes review faster and more accurate.
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.