Methodology
Two kinds of calculation: universal and country-regulated
Some calculators solve math that doesn't depend on any country: percentages, conversions, rule of three, compound interest, mortgages, car or pool consumption. The formula is the same for everyone.
Others calculate something that does depend on a specific country's legislation — a net salary, severance pay, a tax, a social security contribution. These calculators always state their country and currency, and the formula uses that country's regulatory figures (brackets, rates, minimum wages, reference units) instead of a generic formula.
How regulatory figures are stored and reviewed
When a calculation depends on a tax or regulatory figure that doesn't vary from person to person (a tax bracket, a contribution rate, a minimum wage), that figure is centralized in a single place in the code together with the date it became valid and, once re-checked against the official source, the date of the last review — never written loose inside a calculator.
When the figure does vary a lot from person to person (your effective tax rate, a fee that depends on your bank, a regional tax within the same country), the calculator asks you to enter it yourself instead of assuming a default that could be wrong for your case.
Regulatory data is reviewed when there's a known change in the applicable legislation, not on a fixed schedule. A review date shown on a calculator indicates when it was last checked against the official source — not an indefinite guarantee: for an important decision, always verify the figure against the linked official source.
Tools that process files
PDF, image, CSV/Excel and e-invoicing XML tools make no network request with your file: they read it, transform it and produce the result entirely in your browser, using the browser's own APIs (Canvas, File, and libraries loaded only within that tool). The real limit isn't set by Numelto but by your device's memory and power — a very large file may take longer or, on a low-memory device, fail; several tools warn when a file is large instead of promising instant processing at any size.
ID validators: format, not existence
An ID validator only checks that the identifier has the correct structure and check digit — that it “has a valid format”. None of them query the relevant official registry, so none confirm that the identifier is actually assigned, that the person or company exists, or that they're in good standing with the tax or social security authority. A correctly-formatted identifier may not be registered at all, and a mistyped one can, by coincidence, look correctly formatted.
E-invoicing XML tools: interpreting, not officially validating
Tools that read e-invoicing XML formats interpret the file's content and display it in a readable form or convert it to Excel — they don't verify the digital signature, don't query the tax authority, and don't confirm the invoice is still valid or hasn't been cancelled. Being readable here doesn't mean it's valid with the relevant tax authority.
What “indicative result” means
It means the number you see is an estimate based on a simplified formula and the data you entered — not an official document, not a payslip, not a tax return. Every calculator documents its own assumptions in its FAQ section (for example, that a buy-vs-rent simulator assumes a constant home price, or that a net salary calculator doesn't apply personal or family allowances) — these are deliberate simplifications to keep the tool understandable, not mistakes. For decisions that matter, always check an official source or a professional.
Rounding
Results are rounded to 2 decimals in each calculator's currency (euros for Spain, Mexican pesos for Mexico, and so on by country, or the relevant unit for universal calculators). Intermediate calculations, before rounding the final result, use full precision, so two calculators sharing the same formula shouldn't diverge from accumulated rounding.