Thirty-four Italian tax and payroll calculators, free, with the formulas in the open. The server does the arithmetic; the data stays with whoever typed it.
Numica is a calculation site for Italian accountants, payroll advisers and for anyone who has to answer, quickly, a question with a number inside it: what is left in a payslip once you start from the gross annual salary, what an employee really costs the company, what a late tax payment costs once the reduced penalty and the statutory interest are added, whether the flat-rate regime beats the ordinary one, and what a set of financial statements says once the early-warning ratios and the DSCR are computed. It is not a management system, it asks for no account, it keeps no files.
What sets it apart is a matter of method rather than of function. A tax calculator receives data that describe a person or a company: income, children, a home, what is owed to banks and to the revenue. Numica is built so that those data leave no trace. No third-party service loads into the page, no profiling cookie, no log of the inputs. The request comes in, the answer goes out, and nothing is written in between. The rest follows the same rule: every calculator shows its own formulas, the legal sources and the parameters for the year, and every parameter declares the circular or the decree it comes from.
Who it is for. Three recurring uses, and they differ. The professional who has to answer while the client is still on the phone, and cannot open the practice management system for an estimate. The business owner or private individual checking a job offer, a payslip or a rental proposal without booking an appointment for a three-minute question. And whoever is preparing a decision — which hiring incentive to use, whether to distribute profits or leave them in the company, whether to buy a car or lease it — and needs the two scenarios side by side, with the numbers that separate them.
Why it sits in this catalogue. Numica contains no artificial intelligence, and does not pretend otherwise: it is statutory arithmetic, verified case by case. It belongs here because it shows the part of the craft that stays the same when the material changes, the discipline that also holds up the systems where a model really does decide: parameters in one place, formulas in the open, results put to the test before every release, and a data practice that can be described in full on a single page.
What an analysis tool is worth lies not in the ratios it computes, but in what it reads without asking and where the file goes while it reads it.
Since 2010 every Italian limited company has filed its annual accounts with the Business Register in XBRL, under a prime-ministerial decree of December 2008, with a rationale the Register still repeats today: to make the information «immediately usable by third parties». Sixteen years on, in most practices the accounts arrive as a PDF and the figures are retyped by hand into a spreadsheet. The machine-readable file sits in the same folder and nobody opens it.
Numica's statement analysis page starts there. It reads the XBRL instance, fills the form by itself, and computes the early-warning ratios of the Italian national council of accountants against the thresholds for the company's sector, the six-month DSCR and the classic KPIs — EBITDA, ROI, ROE, net financial position — with balance checks on the statement of financial position. Thirty-seven fields, which become zero to type when the file is there.
The reader is code running in the browser, on the machine of whoever uses it. It recognises the schema from the taxonomy reference, identifies the financial year from the context dates, applies the mapping and fills the fields.
What leaves is the ordinary form submission: the same values anyone would have typed by hand. Company name, tax code, registered office and register number stay on the device. Zero bytes of the XBRL file reach the server.
Beside each value sits where it came from: from the file absent not available to be entered. The reader always knows what the machine read and what it did not.
The engine is the same as always, on the server, covered by the same tests. A form filled from the file is indistinguishable from one filled by hand: a fix to the reader changes no figure already computed.
XBRL omits rows that are zero. For nearly every income-statement item, absence is a zero, and treating it so is correct. But in the abbreviated schema — the one used by the large majority of Italian limited companies — liabilities appear only as a total: tax and social-security payables, which feed one of the five ratios, sit in a schedule of the notes that the civil code makes optional. In the micro schema there are no notes at all.
If that schedule was not filled in, the two values do not exist, and no algorithm can invent them. Treating them as zero would produce a false ratio: a warning light switched off that should be on. Telling absent because zero from absent because undeclared is the reader's job, not the file's. Here the field stays empty and the outcome is declared incomplete.
The document Business crisis. The early-warning ratios dates from 20 October 2019. The ministerial decree meant to approve it never came, and the insolvency code in force since 15 July 2022 superseded the whole early-warning system: in its place are the signals on payment arrears and the binding duty to maintain adequate organisational arrangements under article 2086 of the civil code.
They are still computed because they remain the only set of sector thresholds built on a broad sample of Italian accounts, published by an institution, with an explicit hierarchy and written rules even for the edge cases. They are not law: they are documented practice, and must be presented as such. The page says so under every result.
The council's DSCR is forward-looking: it compares the cash flows of the next six months with the principal instalments falling due. It cannot be derived from accounts that describe a year already closed. Many tools compute it anyway with a bank-style formula built on EBITDA and give it the same name: a wrong number under an authoritative label.
Here the four ingredients are asked of whoever uses the tool — opening liquidity, expected inflows, expected
outflows, principal falling due — with the balance-sheet cash position offered as a starting point to update.
All four or none: with three values out of four the calculator returns an error, not an estimate.
For every ratio you see numerator, denominator, value, sector threshold and the direction of the comparison. Not a coloured dot: the fraction the dot would come from. The rules for null denominators are the ones in the document's methodological appendix, applied one by one.
And it also says when there is no alarm: by the document's own account, up to two lit signals out of five the situation is within the sample's norm. A tool that shows a red light without that line makes people read something false.
The hierarchy, in the order it must be read
| Step | What it looks at | What it settles |
|---|---|---|
| 01 | Negative equityAdjusted equity, net of amounts receivable from shareholders and of the reserve for covering losses. | On its own it makes a state of crisis reasonably presumable. The other steps are not needed. |
| 02 | Six-month DSCRExpected flows over principal falling due, from the treasury budget, declared by the user. | Where the forecast data are reliable the DSCR settles it, and the sector ratios stay informational. |
| 03 | Five sector ratiosFinancial charges to revenue · equity to debt · short-term liquidity · cash flow to assets · tax and social-security payables to assets. | The presumption arises only if all five cross the sector threshold. Not one, not three. |
How to read it. The ratios are a 2019 practice reference, no longer required by law after 2022, and the thresholds are calibrated on full-schema accounts of non-micro companies. A ratio between balance-sheet figures is a photograph taken at year end: a crisis, when it comes, shows up in the cash flows of the following months and in payment arrears, which the accounts do not contain. The insolvency code shifted its centre of gravity onto organisational arrangements precisely for that reason. The result is a reading, not a diagnosis, and it must be checked with a qualified professional.
Tax data are personal data. The rule is that the calculation does not keep them.
A browser opening a Numica page talks to exactly one domain: Numica's own. The typefaces are hosted on the same server rather than fetched from an external CDN; there are no third-party analytics scripts, no tracking pixels, no maps, no social widgets. An ad blocker finds nothing to block.
That is why the site has no cookie banner: not because it has been hidden, but because there is no tracking to consent to. The only cookie in circulation is the technical session cookie of the admin area, which an ordinary visitor never meets. The site installs on a phone as an app; even then it stores only fonts, styles and icons, while pages and calculations always go through the server.
Every calculation is a request to the server, which takes the submitted values, runs the calculator's function and returns the result. The controller that receives it writes the inputs neither to a database nor to a log file: income, rent, means-test index, the children's ages, the sale price of a property, the lines of a statement of financial position go in, produce an answer, and are not kept.
What the site does record is that a calculation happened on that calculator, without its values. It is the only measurement needed to know which tools are being used and which are not.
The common pattern on the market is the one where the XBRL file goes up to the server, is processed and sometimes retained. Every upload is a processing operation, every retention a risk, every vendor an external processor with its own contract. It is what you get when the calculation is designed first and privacy only if there is time left.
Here it is designed the other way round. Whoever uploads a set of accounts is telling that site which company they are examining, when, and how urgently: for a professional assessing a client in difficulty that is more sensitive than the figures themselves. The file stays on the device. There is nothing to retain, therefore nothing to protect, therefore nothing to promise.
The analytics are written in house and hosted on the same server: they count pages opened, calculators opened, calculations run and where the visits came from. The IP address is anonymised before it is written, by truncating the last octet, and it is never used to build profiles or to recognise a visitor across two sessions. The detailed log deletes itself after ninety days; only the daily aggregates survive, one number per day and per calculator.
Two features collect information on an explicit request: the star rating after a calculation and the form for asking for a new calculator, which needs an email address in order to reply. Both cap how much a single address can send and keep the data for one year. The privacy notice under article 13 of the GDPR fits on one page, because the processing is small enough to fit there.
A calculator is a pure function, a page that explains it and a test that checks it.
Numica is not a single-page application. Every calculator lives at its own readable address, of the form
/calcolatori/lordo-netto, and the page is assembled by the server with all its content already
in place: title, form, explanation, formulas, legal sources, frequent questions, a worked example, structured
data and related calculators. A search engine, or a conversational assistant that cites its sources, reads the
whole page without running JavaScript. A plain-text index (llms.txt) lists the calculators and tables for conversational assistants.
Reference tables. Five tables for the year, from net salary by gross pay to the cost of an employee, from the flat-rate regime to reverse invoicing and late-payment settlement, are computed by the same engines as the calculators and published on pages of their own, with a commentary on the figures, a CSV file and structured data. When the parameters change, they are regenerated together with the worked examples.
The calculators are grouped into three categories, each with its own index page. The home page is an index of links, not a container of state.
Every calculator is a single PHP file exposing one function: it takes the form fields and returns a table of results. The register of calculators is a configuration file listing, for each one, the identifier, the engine file and the form fields with label, type and whether they are required — including the collapsible advanced blocks, for data only some users have. From that register the site generates the form, the page and the list of permitted calculations.
The controller accepts only identifiers present in the register and loads the corresponding file from that list, never from a value received from outside. Adding a calculator means writing an engine, a register entry and a content entry: three files, with nothing else touched.
Under every result the page shows the formulas applied and the sources: the social-security circular, the ministerial decree, the article of the consolidated act. They are not a plain-language retelling of what the code does: they are the same calculation, written to be read, and when a parameter changes they change with it.
The simplifications are declared at the head of every engine and on the page that accompanies it. A general calculator cannot stand in for a specific national labour contract or a municipal surcharge, and it says so before anyone relies on it.
Every calculator has at least one test case with inputs and expected results worked out by hand from the sources, seventy-three cases in all. Eighteen belong to statement analysis alone: fourteen reference cases, two on the null-denominator rules, one on the partial-DSCR error and one on Italian number formats, with a decimal comma and a thousands dot.
The suite runs from the command line before every release and again on the server afterwards, where a protected page re-runs the same cases against the live environment. A release with one red case does not go live.
Income tax bands, deductions, contribution rates, floors and ceilings, statutory interest rates by year, child benefit amounts, depreciation coefficients, hiring incentives, vehicle tax tariffs, cadastral multipliers, the sector thresholds of the early-warning ratios: everything that changes with the budget law or with a circular sits in a single parameter file, where each block states the rule or the act it comes from. The engines hold no hand-written numbers: they read them from there.
It is a choice paid for once, and it turns every January into a contained operation rather than a hunt for numbers scattered across thirty-four files.
A calculator that does not declare its limits is more dangerous than one that gets a figure wrong, because the error shows and the limit does not. These are written on the pages, next to the results, not at the bottom of a terms-and-conditions page.
A tax calculation is a personal question. The right answer is the one that does not need to remember who asked it.project notes · Numica · October 2026